The Melissa virus, which swept across networks around the world last month, has popped up again in a mutated format, which may have occurred when it inadvertently came in contact with another virus.
The latest variation on the Melissa virus utilises a macro virus to replicate itself across networks as the original did, but now changes the file extension of the Word document from .doc to a RTF format. This may effectively camouflage the virus from antivirus systems that are looking only for the .doc version of the attack. The virus is not actually an RTF document, however, but is simply the Word file masquerading as an RTF file as RTF files cannot contain macro documents.
"An RTF file cannot contain macros, so it cannot contain macro viruses," said Sal Viveros, group marketing manager for Total Virus Defence at Network Associates, which was contacted about the virus by a user. "But with Word you can name your extensions any name you want, so all this virus writer did was change the list.doc in Melissa to list.rtf."
The RTF Melissa virus is similar to the CAP virus which was discovered in 1997 and altered .doc files to RTF files. CAP was summarily added to antivirus application lists to be protected against, but the similarity of the two viruses, and the possible results of an interaction between the two, has also lead Viveros to speculate that the two viruses might have met and mutated in the wild.
If a system infected with CAP virus also contracted Melissa, then CAP could have altered the Melissa files to replicate as RTF files and continued to spread the infection.
"It could have been that someone had the CAP virus on system that got infected by Melissa," said Viveros. "Maybe it was accidental that this was changed to RTF."
However, there is no way to determine if this has been the case, according to Viveros. This new version of the Melissa virus is one of many copycat viruses that have been discovered since the initial outbreak of the virus, which caught national attention.
To protect against the latest version of Melissa, Network Associates and other antivirus vendors recommend that users keep their antivirus lists updated regularly and inform users of the dangers of opening suspicious macros, especially ones fitting the Melissa profile of "Important message from . . ."