A new version of the Melissa virus that crashed computer networks two years ago by clogging up e-mail systems is back, experts warned Friday.

"This virus could become very widespread rapidly," F-Secure Corporation, a Finnish-based software company, said in a statement from its California offices Friday. Melissa.W is a version of Melissa.A, which spread around the world as an e-mail chain letter in March 1999. The virus comes as part of a file named "Anniv.doc" in Microsoft Word 2001 for Macintosh format. "This is problematic, as several anti-virus programs are still unable to handle this new file format, but the file and the virus is fully functional under both Macintosh and Windows versions of Microsoft Office," according to F-Secure. Symantec, an anti-virus software group in Cupertino, Calif., said the new Melissa virus spreads via e-mail with the subject line displaying, "Important Message From (user name)," and text which reads, "Here is that document you asked for ... don't show anyone else;-)." It said Melissa will send the virus to the first 50 people in a user's Microsoft Outlook address book and infect each subsequent document that is opened. The effect would be similar to a Denial of Service attack due to the volume of e-mails created. A 30-year-old computer programmer from New Jersey was charged with creating the Melissa computer virus in 1999.