Computer Viruses and it's Remedy
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What you should know about your computer virus
Virus is almost seen as a destructive agent by almost all the computer users around the globes. In the mid-1980s two brothers in Pakistan discovered that people were pirating their software and as a result they fired-back by writing the first computer virus, a program that would put a copy of itself and a copyright message on any floppy disk copies their customers made. From these simple beginnings, an entire virus counter-culture has emerged. Today new viruses sweep the planet in minutes and can corrupt data, slow networks down, or harm your reputation
Definition of computer virus
Now to go for the real concept and definition of computer virus. A virus or worm is a computer program that can spread across computers and networks by making copies of itself, usually without the user’s knowledge. Viruses can have harmful effects. These can range from displaying irritating messages to stealing data or giving other users control over your computer.
How does computer infected by viruse?
A virus program has to be run before it can infect your computer. Though viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of file. Sometimes they can exploit security flaws in your computer’s operating system to run and to spread themselves automatically. You might receive an infected file in an email attachment, in a download from the internet, or on a disk. As soon as the file is launched, the virus code runs. Then the virus can copy itself to other files or disks and make changes on your computer.
Trojan horses
Trojan horses are programs that pretend to be legitimate software, but actually carry out hidden, harmful functions. For example, DLoader-L arrives in an email attachment and claims to be an urgent update from Microsoft for Windows XP. If you run it, it downloads a program that uses your computer to connect to certain websites, in an attempt to overload them (this is called a denial of service attack). Trojans cannot spread as fast as viruses because they do not make copies of themselves. However, they now often work hand-in-hand with viruses. Viruses may download Trojans which record keystrokes or steal information. On the other hand, some Trojans are used as a means of infecting a computer with a virus.
Worms
Worms are similar to viruses but do not need a carrier program or document. Worms simply create exact copies of themselves and use communications between computers to. Many viruses, such as MyDoom or Bagle, behave like worms and use email to forward themselves.
What can viruses do?
Viruses used to play pranks or stop your computer working, but now they compromise security in more
insidious ways. Here are the things that viruses can do.
■ Slow down email. Viruses that spread by email, such as Sobig, can generate so much email traffic that servers slow down or crash. Even if this doesn't happen, companies may react to the risk by shutting down servers anyway.
■ Steal confidential data. The Bugbear-D worm records the user's keystrokes, including passwords, and gives the virus writer access to them.
■ Use your computer to attack websites.
MyDoom used infected computers to flood the SCO software company's website with data, making the site unusable (a denial of service attack).
■ Let other users hijack your computer. Some viruses place “backdoor Trojans” on the computer, allowing the virus writer to connect to your computer and use it for their own purposes.
■ Corrupt data. The Compatable virus makes changes to the data in Excel spreadsheets.
■ Delete data. The Sircam worm may attempt to delete or overwrite the hard disk on a certain day.
■ Disable hardware. CIH, also known as Chernobyl, attempts to overwrite the BIOS chip on April 26, making
the computer unusable.
■ Play pranks. The Netsky-D worm made computers beep sporadically for several hours one morning.
■ Display messages. Cone-F displays a political message if the month is May.
■ Damage your credibility. If a virus forwards itself from your computer to your customers and business partners,
they may refuse to do business with you, or demand compensation.
■ Cause you embarrassment. For example, PolyPost places your documents and your name on sex related newsgroups.
Where are the virus risks?
Viruses can reach your computer via all the routes shown here. You can read more details on the pages that follow.
CDs and floppies
Floppy disks can have a virus in the boot sector. They can also hold infected programs or documents. CDs may also hold infected items.
Programs and documents
Programs and documents can be infected with viruses. When you share them with other users, by putting them on your network or intranet, or by sending them out, the infection can spread.
Email
Email can include infected attachments. If you double click on an infected attachment, you risk infecting your machine. Some emails even include malicious scripts that run as soon as you preview the mail or read the body
text.
The internet
You may download programs or documents that are infected. Security vulnerabilities in your operating system can
also allow viruses to infect your computer via the internet connection, without your having to do anything at all
Email viruses
Many of the most prolific viruses are email-aware: they distribute themselves automatically by email.
Typically, email-aware viruses depend on the user clicking on an attached document. This runs a script that can forward infected documents to other people. The Netsky virus, for example, searches the computer for files that may
contain email addresses (e.g. EML or HTML files), and then uses the email program on your computer to send
itself to those addresses. Some viruses, like Sobig-F, don’t even need to use your email browser; they include their own “SMTP engine” for sending mail. Email viruses may compromise your computer’s security or steal data, but their most common effect is to create excessive email traffic and crash servers.
Email attachments
Any attachment that you receive by email could carry a virus; launching such an attachment can infect your
computer. Even an attachment that appears to be a safe type of file, e.g. a file with a .txt extension, can pose a threat.
That file may be a malicious VBS script with the real file type (.vbs) hidden from view
Viruses, Trojans and worms
In the mid-1980s two brothers in Pakistan discovered that people were pirating
their software. They responded by writing the first computer virus, a program that
would put a copy of itself and a copyright message on any floppy disk copies their customers made. From these simple beginnings, an entire virus counter-culture has emerged. Today new viruses sweep the planet in minutes and can corrupt data, slow networks down, or harm your reputation.
Which files can viruses infect?
Viruses can attach themselves to any code that runs on your computer: programs, documents, or the files that start up the operating system.
Boot sectors
When you switch on your computer, it accesses a part of the disk called the “boot sector”and runs a program that starts the operating system. The earliest viruses replaced this boot sector with their own, modified version. If the user started up their computer from an infected disk, the virus became active.
Programs
Some viruses infect programs. When you start the infected program, the virus is launched first. This type of virus appeared early in virus history but still poses a threat, as the internet makes it easy to distribute programs.
Documents
Word processing or spreadsheet applications often use “macros” to automate tasks. Some viruses take the form of a macro that can spread from one document to another. If you open a document that contains the virus, it copies itself into the application’s startup files and infects other documents you open with that application.
Preventing viruses
There are simple measures you can take to avoid being infected or to deal with viruses if you are infected. For more details, see the “Tips for safer computing” chapter.
Make users aware of the risks Tell everyone that they are at risk if they open email attachments, download files from websites, or swap disks.
Install anti-virus software and update it regularly Anti-virus programs can detect and often disinfect viruses. If the software offers on-access virus checking, use it.
Use software patches to close security loopholes Watch out for “patches” for your operating system. These often close loopholes that make you vulnerable to viruses.
Use firewalls A firewall can prevent unauthorized access to your network and also prevent viruses sending out information.
Keep backups of all your data Keep backups of all data and software, including operating systems. If you are affected by a virus, you can replace your files and programs with clean copies.
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completely usless in a twinkle of an eye.Computer 
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