A virus that first surfaced late last week is threatening to slow Internet mail transmissions to a crawl today as employees return to work. Late in the day Friday, the Computer Emergency Response Team (CERT) at Carnegie Mellon University began receiving reports that a macro virus propagating through E-mail attachments was infecting computer systems running Microsoft Word 97 and Word 2000.

The virus, dubbed Melissa, is activated by users who unknowingly invoke a macro when they open what appears to be a normal Word attachment that contains the virus. The virus allegedly sends 50 mail messages, each containing a list of pornographic Web sites. Melissa is transported in the form of an E-mail, typically carrying a subject header that reads "Important Message."

The danger, CERT says in its advisory, is that once the E-mail is opened it can continually propagate, flooding E-mail servers and slowing down communications. CERT also cautions that while the chief transmission mode is E-mail, any mechanism for moving files can transmit the virus.

CERT says users should not open messages with "Important Message" in the subject header. The group also advised users disable the "macro" function in Word.

Users and IT professionals can download patch antidotes from their antivirus providers' Web sites. Continual updates and more details about Melissa are available at http://www.cert.org/advisories/CA-99-04-Melissa-Macro-Virus.html and http://www.avertlabs.com/public/datafiles/valerts/vinfo/melissa.asp.