Antivirus firms have warned users to watch out for a comedy email featuring a caricature of ex-President Bill Clinton - not because it's funny, but because it's a virus.

Already reported in the wild, Caricature arrives as an email with the subject "bill caricature" and an attachment screensaver, cari.scr.

If the attachment is opened users are greeted with a cartoon of Bill Clinton playing a saxophone from which a bra is emerging.

But in the background, the program is emailing a copy of the virus to every name found in the Windows Address Book.

Text at the end of infected emails reads: "No viruse [sic] found - McAfee". But this is simply social engineering in an effort to lure the user into a false sense of security.

"Fortunately, the terrible spelling in this worm's message will leave well-informed users in no doubt that this email is one to be avoided. Those practising safe computing should not be caught out," said Natasha Staley, antivirus consultant at Sophos.