You can get more and more pernickety definitions of what is and what isn’t a computer virus, depending on how pedantic you are and how much of a techy you are. What many people call a virus may in fact be a trojan, a worm, an eggdrop, a mailbomb… For most people the attitude when confronted with all this terminology is “as long as you know what I mean, who cares?”
The answer is: you care. At least, you care if it makes a difference between simply deleting an email or having to re-install your hard drive.
For the purposes of this post, a computer virus is defined as a computer program that multiplies and spreads, occupying IT resources[1].
To confuse the issue, there is the concept of “viral” marketing. This usually indicates a piece of video footage or other material that people (NOTE: people, not computers) find so compelling that they send it to all their friends, thus spreading in a similar pattern to that of a virus.
The marketing world adopted, rather than invented, this technique. Many hoaxes have appeared over the years that spread like this. What we nowadays call a “mail virus” in the old day was called a “rumour”.
Example: The ICE email. It “went viral”. It seemed like a good idea, and it had all the emotion of the 7/7 bombings behind it. So lots of people got multiple copies of it, and it became nearly as annoying a Crazy Frog. But it is NOT a virus! By rumour and hearsay, people are believing that somehow entering an ICE entry in your phone leaves you open to attack. For the vast majority of phone users, this is not true. Do NOT delete your ICE entry from your phone solely on account of this rumour!
The way to spot one of these mails is simply that you feel a compulsion to forward it. Maybe it’s an alert about somebody putting AIDs-infected needles in cinema seats, asking you to identify a tsunami victim thought to be from around your area, or ironically, a warning about a virus that doesn’t actually exist.
The giveaway is when the text of the message says “COPY THIS TO EVERYONE YOU KNOW!” that, my friends, is exactly how this type of “virus” spreads.
Often they carry phrases like “This is TRUE! It happened to my friend!” etc. Ask yourself whose friend? The person who sent it to you? The person who sent it to them? Someone else? Or maybe it didn’t happen to anybody’s friend.
Ask yourself when will this mail expire? If it’s a collection for a raffle on St. David’s day 2006, then you know it’s going to run for a year at the max. If however it has no expiry, there’s no reason for it to ever stop. Even if it’s not a hoax, it has the potential to go viral.
Most virus databases keep records of known viral emails because although the technology is very different, the social impact is much the same. Google for virus database then click through and use the site’s search to see whether your email is known, for example: http://securityresponse.symantec.com/avcenter/venc/data/the.new.ice.age.hoax.html
[1] On a techy note, that’s not really what a virus is at all. If the program spreads from computer to computer across a network, it’s a worm. If you’re at a party and want to impress a handsome geek, say “worm” rather than “virus”.