One network administrator said he first spotted the renamed virus in an email with the subject header "Fwd: Joke" around noon today.
Antivirus software aimed at neutralizing I Love You may not work against Very Funny, administrators said. Utilities written to filter out I Love You based on name alone will not work.
Some security software providers are issuing new patches designed to include protection against the Very Funny variant.
"It seems to be that someone has changed the name of the attachment and the subject line," said Nerender Mangalan, director of security strategy for Computer Associates. "Basically it's the exact same file, and it does the exact same thing, but it's renamed so people looking out for I Love You would open it."
Computer Associates said it would post its updated patch by around 3 p.m. PT.
Representatives from Microsoft said they had no information about the new variation of the virus.
Some network administrators said other software patches were effective against Very Funny.
"We deleted all the emails with I Love You in the header," said Carmelo Lisciotto, director of network operations for online auction site uBid. "We got the first email this morning, and we ran some command-line utilities to delete anything with that header."
Those filters failed to detect Very Funny.
But Lisciotto said antivirus software designed by Microsoft and Symantec for I Love You did work against Very Funny.
The origin of Very Funny, like that of I Love You, remains obscure. But Lisciotto and others were skeptical that the virus was written to rename itself.
"Personally, I think someone re-sent it," Lisciotto said.