Cheat Sheet: Computer viruses

I think I know but what actually is a computer virus?
A computer virus is a program designed to spread itself by first infecting executable files or the system areas of hard and floppy disks and then making copies of itself.

What kind of files spread viruses?
Viruses can infect any type of executable code - not just program files. Some viruses infect code in the boot sector of floppy disks or in system areas of hard drives. Another type of virus, known as a macro virus, can infect word processing and spreadsheet documents that use macros. It's also possible for HTML documents containing JavaScript or other types of code to spread viruses.

How do they spread?
When you run an infected program, the virus code activates and will try to infect other programs, either on the same computer or on other computers connected to it over a network. Those newly infected programs then try to infect yet more programs... but you get the picture.

What harm can they do?
Viruses are software programs and they can do the same things as any other programs. The actual effect of any particular virus depends on the (usually malicious) mood of its writer. Some viruses are deliberately designed to damage files or otherwise interfere with your computer's operation, while others don't do anything but try to spread themselves around. But even these 'harmless' ones can cause damage, since they affect files and jam up networks.

Hold on. So what's a worm? We hear all about them now too.
A worm is similar to a virus but has the ability to start replicating without being manually activated using parts of an OS which are automatic and usually invisible to the user. Quite often a worm is only noticed when its activity consumes system resources, slowing down other tasks.

And a Trojan horse?
A Trojan horse is not a virus but simply a program that pretends to be something else. For example, you might download what you think is a new game but when you run it, it deletes files on your hard drive or emails your saved passwords to another person.

How do I spot a virus hoax?
Hoaxes normally threaten some form of far-fetched impending catastrophe - like your computer blowing up - and tell you to forward the warning to everybody in your address book. IF In DOUBT, LOOK FOr UnneCESSARy CAPitALs and EXClaMATION MARKs!!!!!!!!!!!!! Or check the library of hoaxes on any reputable anti-virus vendor's site.

I might know more now but how do I avoid getting infected?
The easy answer to this is to buy anti-virus software for your computer or network. Unfortunately, however, the speed at which new viruses are written means the software needs to be updated regularly (and even then it's not foolproof).

A second line of defence is to treat email attachments with suspicion: save attachments to disk and then check with a virus scanner before opening the file. If you can't positively verify what one is, who it came from and why it was sent to you, then proceed with extreme caution.

Headline-grabbing outbreaks such as Melissa and Love Bug demonstrate that just because an email appears to come from someone you trust, it doesn't mean it's safe.

Be vigilant!

Tell us what you think by posting a Reader Comment or emailing editorial@silicon.com

**Essential Links**
From the silicon.com archive
'Death of the internet' warning issued
http://www.silicon.com/a51279
Security still not on the agenda for IT directors
http://www.silicon.com/a50841
Time for proactive anti-virus tools
http://www.silicon.com/a50811

External Links
http://www.vmyths.com
http://www.sophos.co.uk
http://www.nai.com
http://www.symantec.com

CS1