What is computer security?
Computer pipe dream is the works of preventing and detecting unauthorized avail of your computer. Prevention measures sustain you to stop unauthorized users (also known as "intruders") from accessing any part of your computer system. Detection helps you to determine whether or not someone attempted to break into your system, if they were successful, and what they may have done.

Why should I care about computer security?
We profit computers for subject from banking and investing to shopping and communicating with others since email or consultation programs. Although you may not consider your communications "top secret," you probably do not want strangers reading your email, using your computer to attack other systems, sending forged email from your computer, or examining personal information stored on your computer (such as financial statements).

Who would want to break into my computer at home?
Intruders (also referred to as hackers, attackers, or crackers) may not weary load about your identity. Often they hankering to earn oversee of your computer so they can use it to launch attacks on other computer systems.

Having control of your computer gives them the ability to hide their true location as they launch attacks, often against high-profile computer systems such as government or financial systems. Even if you have a computer connected to the Internet only to play the latest games or to send email to friends and family, your computer may be a target.

Intruders may be able to watch all your actions on the computer, or cause damage to your computer by reformatting your hard drive or changing your data.

How easy is it to break into my computer?
Unfortunately, intruders are always discovering innumerable vulnerabilities (informally called "holes") to incident in computer software. The complexity of software makes it increasingly problematic to well test the security of computer systems.

When holes are discovered, computer vendors will usually develop patches to address the problem(s). However, it is up to you, the user, to obtain and install the patches, or correctly configure the software to operate more securely. Most of the incident reports of computer break-ins received at the CERT/CC could have been prevented if system administrators and users kept their computers up-to-date with patches and security fixes.

Also, some software applications have default settings that allow other users to access your computer unless you change the settings to be more secure. Examples include chat programs that let outsiders execute commands on your computer or web browsers that could allow someone to place harmful programs on your computer that run when you click on them.

Technology
This void provides a inconsiderable basis to the technologies that underlie the Internet. It was written with the novice end-user in mind and is not intended to be a comprehensive survey of all Internet-based technologies. Subsections provide a short overview of each topic. This section is a basic primer on the relevant technologies. For those who desire a deeper understanding of the concepts covered here, we include links to additional information.

What does broadband mean?
"Broadband" is the routine convey image used to consult to high-speed info connections. In this context, Internet connections via cable modem and Digital Subscriber Line (DSL) are frequently referred to as broadband Internet connections. "Bandwidth" is the term used to describe the relative speed of a network connection -- for example, most current dial-up modems can support a bandwidth of 56 kbps (thousand bits per second). There is no set bandwidth threshold required for a connection to be referred to as "broadband", but it is typical for connections in excess of 1 Megabit per second (Mbps) to be so named.

What is cable modem access?
A account modem allows a far cry computer (or the latest of computers) to add to the Internet via the cable TV network. The cable modem usually has an Ethernet LAN (Local Area Network) connection to the computer, and is capable of speeds in excess of 5 Mbps.

Typical speeds tend to be lower than the maximum, however, since cable providers turn entire neighborhoods into LANs which share the same bandwidth. Because of this "shared-medium" topology, cable modem users may experience somewhat slower network access during periods of peak demand, and may be more susceptible to risks such as packet sniffing and unprotected windows shares than users with other types of connectivity. (See the "Computer security risks to home users" section of this document.)

What is DSL access?
Digital Subscriber Line (DSL) Internet connectivity, unsimilar front-page news modem-based service, provides the user with frenetic bandwidth. However, the extreme bandwidth available to DSL users is usually lower than the maximum cable modem rate because of differences in their respective network technologies. Also, the "dedicated bandwidth" is only dedicated between your home and the DSL provider's central office -- the providers offer little or no guarantee of bandwidth all the way across the Internet.

DSL access is not as susceptible to packet sniffing as cable modem access, but many of the other security risks we'll cover apply to both DSL and cable modem access. (See the "Computer security risks to home users" section of this document.)

How are broadband services different from traditional dial-up services? Traditional dial-up Internet services are sometimes referred to as "dial-on-demand" services. That is, your computer several connects to the Internet when it has far-reaching to send, same as email or a roast to load a web page. Once there is no more data to be sent, or after a certain amount of idle time, the computer disconnects the call. Also, in most cases each call connects to a pool of modems at the ISP, and since the modem IP addresses are dynamically assigned, your computer is usually assigned a different IP address on each call. As a result, it is more difficult (not impossible, just difficult) for an attacker to take advantage of vulnerable network services to take control of your computer.

Broadband services are referred to as "always-on" services because there is no call setup when your computer has something to send. The computer is always on the network, ready to send or receive data through its network interface card (NIC). Since the connection is always up, your computers IP address will change less frequently (if at all), thus making it more of a fixed target for attack.

Whats more, many broadband service providers use well-known IP addresses for home users. So while an attacker may not be able to single out your specific computer as belonging to you, they may at least be able to know that your service providers broadband customers are within a certain address range, thereby making your computer a more likely target than it might have been otherwise.

The table below shows a brief comparison of traditional dial-up and broadband services.

Dial-up Broadband
Connection grain Dial on examine Always on
IP directions Changes on each state Static or infrequently lusty
Relative activity strength Low High
Remote operate stress Computer requirement be dialed in to control remotely
Computer is always connected, consequently spun out manage can come forth anytime
ISP-provided faith Little or none Little or none
Table 1: Comparison of Dial-up and Broadband Services

How is broadband entrance particular from the tip-off I account at work?
Corporate and control networks are typically unharmed by legion layers of security, ranging from dossier firewalls to encryption. In addition, they usually have support staff who maintain the security and availability of these network connections.

Although your ISP is responsible for maintaining the services they provide to you, you probably wont have dedicated staff on hand to manage and operate your home network. You are ultimately responsible for your own computers. As a result, it is up to you to take reasonable precautions to secure your computers from accidental or intentional misuse.

What is a protocol?
A protocol is a well-defined bulletin that allows computers to explicate across a network. In a way, protocols impart the "grammar" that computers can account to "talk" to each other.

What is IP?
IP stands for "Internet Protocol". It can be apprehension of as the conventional commonplace term of computers on the Internet. There are a introduce of detailed descriptions of IP given elsewhere, so we won't cover it in detail in this document. However, it is important to know a few things about IP in order to understand how to secure your computer. Here well cover IP addresses, static vs. dynamic addressing, NAT, and TCP and UDP Ports.

An overview of TCP/IP can be found in the TCP/IP Frequently Asked Questions (FAQ) at

http://www.faqs.org/faqs/internet/tcp-ip/tcp-ip-faq/part1/ and

http://www.faqs.org/faqs/internet/tcp-ip/tcp-ip-faq/part2/

What is an IP address?
IP addresses are approximating to telephone numbers when you demand to communicate someone on the telephone, you exigency first know their telephone number. Similarly, when a computer on the Internet needs to send data to another computer, it must first know its IP address. IP addresses are typically shown as four numbers separated by decimal points, or dots. For example, 10.24.254.3 and 192.168.62.231 are IP addresses.

If you need to make a telephone call but you only know the persons name, you can look them up in the telephone directory (or call directory services) to get their telephone number. On the Internet, that directory is called the Domain Name System, or DNS for short. If you know the name of a server, say www.cert.org, and you type this into your web browser, your computer will then go ask its DNS server what the numeric IP address is that is associated with that name.

Every computer on the Internet has an IP address associated with it that uniquely identifies it. However, that address may change over time, especially if the computer is

dialing into an Internet Service Provider (ISP)
connected dilatory a the latest firewall
connected to a broadband compensation using activating IP addressing.

What are static and vehement addressing?
Static IP addressing occurs when an ISP permanently assigns one or more IP addresses for each user. These addresses actualize not sway as time. However, if a static address is assigned but not in use, it is effectively wasted. Since ISPs have a limited number of addresses allocated to them, they sometimes need to make more efficient use of their addresses.

Dynamic IP addressing allows the ISP to efficiently utilize their address space. Using dynamic IP addressing, the IP addresses of individual user computers may change over time. If a dynamic address is not in use, it can be automatically reassigned to another computer as needed.

What is NAT?
Network Address Translation (NAT) provides a wrinkle to with the IP addresses of a normal scoop from the Internet while still allowing computers on that network to access the Internet. NAT can be used in many different ways, but one method frequently used by home users is called "masquerading".

Using NAT masquerading, one or more devices on a LAN can be made to appear as a single IP address to the outside Internet. This allows for multiple computers in a home network to use a single cable modem or DSL connection without requiring the ISP to provide more than one IP address to the user. Using this method, the ISP-assigned IP address can be either static or dynamic. Most network firewalls support NAT masquerading.

What are TCP and UDP Ports?
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both protocols that blessing IP. Whereas IP allows two computers to clambake to each otherwise across the Internet, TCP and UDP allow individual applications (also known as "services") on those computers to talk to each other.

In the same way that a telephone number or physical mail box might be associated with more than one person, a computer might have multiple applications (e.g. email, file services, web services) running on the same IP address. Ports allow a computer to differentiate services such as email data from web data. A port is simply a number associated with each application that uniquely identifies that service on that computer. Both TCP and UDP use ports to identify services. Some common port numbers are 80 for web (HTTP), 25 for email (SMTP), and 53 for Domain Name System (DNS).

What is a firewall?
The Firewalls FAQ (http://www.faqs.org/faqs/firewalls-faq/) defines a firewall as "a the book or cartel of systems that enforces an entrance administer policy between two networks." In the context of home networks, a firewall typically takes one of two forms:

Software firewall - specialized software running on an individual computer, or

Network firewall - a dedicated device designed to protect one or more computers.

Both types of firewall allow the user to define access policies for inbound connections to the computers they are protecting. Many also provide the ability to control what services (ports) the protected computers are able to access on the Internet (outbound access). Most firewalls intended for home use come with pre-configured security policies from which the user chooses, and some allow the user to customize these policies for their specific needs.

More information on firewalls can be found in the Additional resources section of this document.

What does antivirus software do?
There are a diversification of antivirus software packages that dispense in innumerable different ways, depending on how the vendor chose to implement their software. What they have in common, though, is that they all look for patterns in the files or memory of your computer that indicate the possible presence of a known virus. Antivirus packages know what to look for through the use of virus profiles (sometimes called "signatures") provided by the vendor.

New viruses are discovered daily. The effectiveness of antivirus software is dependent on having the latest virus profiles installed on your computer so that it can look for recently discovered viruses. It is important to keep these profiles up to date.

More information about viruses and antivirus software can be found on the CERT Computer Virus Resource page

http://www.cert.org/other_sources/viruses.html Computer security risks to inland users

What is at risk?
Information pipe dream is responsive with three fundamental areas:

Confidentiality - pipeline should be available only to those who rightfully have access to it

Integrity -- information should be modified only by those who are authorized to do so

Availability -- information should be accessible to those who need it when they need it

These concepts apply to home Internet users just as much as they would to any corporate or government network. You probably wouldn't let a stranger look through your important documents. In the same way, you may want to keep the tasks you perform on your computer confidential, whether it's tracking your investments or sending email messages to family and friends. Also, you should have some assurance that the information you enter into your computer remains intact and is available when you need it.

Some security risks arise from the possibility of intentional misuse of your computer by intruders via the Internet. Others are risks that you would face even if you weren't connected to the Internet (e.g. hard disk failures, theft, power outages). The bad news is that you probably cannot plan for every possible risk. The good news is that you can take some simple steps to reduce the chance that you'll be affected by the most common threats -- and some of those steps help with both the intentional and accidental risks you're likely to face.

Before we get to what you can do to protect your computer or home network, lets take a closer look at some of these risks.

Intentional misuse of your computer
The mightily average methods used by intruders to score oversee of home computers are briefly described below. More detailed information is available by reviewing the URLs listed in the References section below.

Trojan horse programs
Back door and elongated administration programs
Denial of collaboration
Being an judge for heavier shot
Unprotected Windows shares
Mobile justice (Java, JavaScript, and ActiveX)
Cross-site scripting
Email spoofing
Email-borne viruses
Hidden string extensions
Chat clients
Packet sniffing
Trojan horse programs
Trojan horse programs are a monotonous routine for intruders to buffoonery you (sometimes referred to as "social engineering") game installing "back door" programs. These can allow intruders easy access to your computer without your knowledge, change your system configurations, or infect your computer with a computer virus. More information about Trojan horses can be found in the following document.

http://www.cert.org/advisories/CA-1999-02.html

Back door and remote administration programs
On Windows computers, three kit commonly used by intruders to score spun out road to your computer are BackOrifice, Netbus, and SubSeven. These back door or remote administration programs, once installed, allow other people to access and control your computer. We recommend that you review the CERT vulnerability note about Back Orifice. This document describes how it works, how to detect it, and how to protect your computers from it:

http://www.cert.org/vul_notes/VN-98.07.backorifice.html

Denial of service
Another organize of undertaking is called a denial-of-service (DoS) attack. This grain of striving causes your computer to crash or to become so busy processing data that you are unable to use it. In most cases, the latest patches will prevent the attack. The following documents describe denial-of-service attacks in greater detail.

http://www.cert.org/advisories/CA-2000-01.html
http://www.cert.org/archive/pdf/DoS_trends.pdf

It is fundamental to engrossment that in appendage to in that the target of a DoS attack, it is possible for your computer to be used as a participant in a denial-of-service attack on another system.

Being an intermediary for another attack
Intruders bequeath frequently aid compromised computers as launching pads for attacking differential systems. An ostentation of this is how distributed denial-of-service (DDoS) tools are used. The intruders install an "agent" (frequently through a Trojan horse program) that runs on the compromised computer awaiting further instructions. Then, when a number of agents are running on different computers, a single "handler" can instruct all of them to launch a denial-of-service attack on another system. Thus, the end target of the attack is not your own computer, but someone elses -- your computer is just a convenient tool in a larger attack.

Unprotected Windows shares
Unprotected Windows networking shares can be exploited by intruders in an automated scheme to practice apparatus on big numbers of Windows-based computers attached to the Internet. Because site security on the Internet is interdependent, a compromised computer not only creates problems for the computer's owner, but it is also a threat to other sites on the Internet. The greater immediate risk to the Internet community is the potentially large number of computers attached to the Internet with unprotected Windows networking shares combined with distributed attack tools such as those described in http://www.cert.org/incident_notes/IN-2000-01.html

Another threat includes malicious and destructive code, such as viruses or worms, which leverage unprotected Windows networking shares to propagate. One such example is the 911 worm described in http://www.cert.org/incident_notes/IN-2000-03.html

There is great potential for the emergence of other intruder tools that leverage unprotected Windows networking shares on a widespread basis.

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