E-mail Viruses

The latest thing in the world of computer viruses is the e-mail virus, and the Melissa virus in March 1999 was spectacular. Melissa spread in Microsoft Word documents sent via e-mail, and it worked like this: someone created the virus as a Word document uploaded to an Internet newsgroup. Anyone who downloadedthe document and opened it would triggerthe virus. The virus would men send the document (and therefore itself) in an e-mail message to the first 50 people in the person's address book. The e-mail message contained a friendly note that included the person's name, so the recipientwould open the document thinking it was harmless. The virus would then create 50 new messages from the recipient's machine. As a result, the Melissa virus was the fastest-spreading virus ever seen! As mentioned earlier, it forced a number of large companies to shut down their e-mail systems.

The ILOVEYOU virus, which appeared on May 4, 2000, was even simpler. It contained a piece of code as an attachment. People who double clicked on the attachment allowed the code to execute. The code sent copies of itself to everyone in the victim's address book and then started corrupting files on the victim's machine. This was the simplest thing the virus could do. It was really more of a Trojan horse distributed by e-mail than it was a virus. The Melissa virus took advantage of the programming language built into Microsoft Word called VBA, or Visual Basic for Applications. It is a complete programming language and it can be programmed to do things like modify files and send e-mail messages. It also has a useful but dangerous auto-execute feature. A programmer can insert a program into a document that runs instantly whenever the document is opened. This is how the Melissa virus was programmed. Anyone who opened a document infected with Melissa would immediately activate the virus. It would send the 50 e-mails, and then infect a central file called NORMAL.DOT so that any file saved later would also contain the virus! It created a huge mess.

Microsoft applications have a feature called Macro Virus Protection built into them to prevent this sort of thing. With Macro Virus Protection turned on (the default option is ON), its auto-execute feature is disabled. So when a document tries to auto-execute viral code, a dialog pops up warning the user. Unfortunately, many people don't know what macros or macro viruses are, and when they see the dialog they ignore it, so the virus runs anyway. Many other people turn off the protection mechanism. So the Melissa virus spread despite the safeguards in place to prevent it.