There is a further class of "viruses," which is unique, in that it comprises viruses that don't exist as computer code. The term meme seems to have been coined originally by Richard Dawkins, whose paper Viruses of the Mind draws on computer virology as well as on the natural sciences. A meme is a unit of cultural transmission, of replication by imitation, much as a gene is a unit of inheritance (a rather imprecise unit, perhaps). The memes we are most concerned with in this article are those sometimes known as metaviruses. A metavirus is itself a virus (what Dawkins calls a "virus of the mind, not a computer virus"), but purports to deal with other viruses (which are computer viruses). These viruses don't happen to exist. In other words, they are virus hoaxes. Virus hoaxes are not only a subclass of memes in general, but a subset of a particular type of meme, the chain letter. However, the virus hoax is particularly relevant to this article, because the administrator who manages virus incidents will usually also be the person who has to respond to plagues of virus hoaxes. The same might not be true of other hoaxes and chain letters.

The most commonly encountered hoaxes are derived from the infamous Good Times hoax of the mid-1990s. They conform to a pattern something like this:

[THIS WARNING WAS CONFIRMED BY SYMANTEC AND MCAFEE THIS MORNING.] IF YOU RECEIVE EMAIL WITH THE SUBJECT <GREEN EGGS AND HAM> DO NOT OPEN IT, BUT DELETE IT IMMEDIATELY!!! IT CONTAINS A VIRUS THAT JUST BY OPENING THE MESSAGE TRASHES HARD DRIVES AND CAUSES MOUSE-MATS TO SPONTANEOUSLY COMBUST. MICROSOFT, AOL, IBM, FCC, NASA, CND, AND KKK HAVE ALL SAID THAT THIS IS A VERY DANGEROUS VIRUS !!! AND THERE IS NO REMEDY FOR IT AS YET. PLEASE FORWARD THIS TO ALL YOUR FRIENDS, RELATIVES, COLLEAGUES, AND ANYONE ELSE WHOSE EMAIL ADDRESS YOU HAVE HANDY SO THAT THIS DISASTER CAN BE AVERTED.

By the way, as far as I know there is no Green Eggs and Ham virus or hoax. I've just done what many real hoaxers have done and pulled a silly title out of thin air (or in this case my daughter's bookshelf). In fact, the infuriating aspect of this problem is that most hoaxers are abominably lazy and unoriginal, and the subject of the email which carries the supposed virus is often the only bit of the hoax that varies between two variants.

This sort of hoax only continues to work because masses of people with little technical knowledge of computers (let alone computer viruses) join the Internet community for the first time every day. Each one is at high risk of passing on such a hoax because they don't know any better. Of course, a hoax can be much more subtle than this, but I'm not here to tell you how to write a hoax that might fool even an expert.

Here are a few of the features that would alert the experienced hoax watcher to the unreliability of the Green Eggs and Ham alert:

· Uppercase is used throughout and the message carries clusters of exclamation marks for emphasis. This doesn't, of course, prove anything about the accuracy of the alert. Nevertheless, it's been observed many times that use of uppercase, liberal exclamation marks, and poor spelling, grammar and style characterize most of the common hoaxes. On no account, however, should you assume that an alert is accurate simply because it doesn't have these characteristics.

· The reference to McAfee and Symantec doesn't give contact or reference information. It's just there to add credibility to the hoax. There's no real indication of when it was written, either. There are hoaxes circulating the Internet right now, saying that IBM announced something "yesterday," that have been around for years. The "yesterday" is just there to give a false impression of urgency.

· It's true that some email viruses/worms arrive with a characteristic subject header. However, there are many others that don't, and it makes more sense to avoid executing any attachment than to try to remember which silly header goes with which virus. In fact, administrators trying to block particular viruses by filtering mail on subject alone and using inappropriate criteria are responsible for a whole subclass of indirect Denial of Service (DoS) attacks in and on themselves.

· It makes sense to be cautious about email, but just opening a message can only infect your system if you have certain mail programs (Outlook, primarily) set with incautious defaults. Most mailers don't execute code just by viewing the message. An alert that says that this will happen but doesn't specify any particular mailer, should be regarded with suspicion.

· It's implied that the malicious code works on any hardware. This is pretty suspicious. What's more, a payload that triggered as soon as you opened the message/attachment would be pretty ineffective at spreading. You might think the mouse-mat payload is a bit over the top. Actually, real hoaxes are often as ridiculous as this (although they often conceal their improbability behind technobabble).

· Of all the organizations listed, only IBM has any real expertise in viruses. The others are only listed to impress you.

· It's claimed that there is no "remedy" for the virus. Anti-virus vendors can usually supply fixes for new viruses in hours, even minutes. Of course, the effects of some viruses might be impossible to reverse, but data recovery firms can perform near-miracles sometimes.

· A virus that trashes your system as soon as you execute it is unlikely to travel very far. What is being described here sounds more like a destructive Trojan, and they don't generally spread well through email.

· The warning urges you to forward the mail to everyone you know. That makes it a chain letter. Reputable and knowledgeable organizations don't send alerts that way, although clueless ones sometimes do.