A computer virus on the Internet can spread more quickly than a biological one in the physical world. Here, too, keeping a new virus out of the corporate network is much easier than trying to eradicate one that's already infiltrated it.
Macro viruses infect and spread by means of macros associated with office-automation applications.
These macros usually are stored as part of a document and can be transported easily as attachments to e-mail messages. On the morning of March 26, the first incidents of the Melissa macro virus were reported in the United States. By the end of the day many sites were infected. In fact, Melissa spread so quickly that the virus easily could have been inside your network before you had a chance to update antivirus gateway software, which highlights the gateway's role of augmenting rather than replacing internal antivirus protection on servers and client workstations. Melissa served as a useful wake-up call, reminding us that the virus threat continues to evolve.