Virus researchers at Sophos have warned users that a new in-the-wild worm, Netsky-AC (W32/Nestky-AC), is posing as a cure for the fast-spreading Sasser worm.
Attached to emails generated by Netsky-AC is a file which claims to come from an anti-virus company, and to be a fix for the Sasser worm.
With the Sasser worm spreading quickly around the world, infecting internet users and generating headlines in the media, Sophos is concerned that some users may fall for Netsky-AC's trick and launch its damaging payload.
"This latest Netsky worm arrives via email, pretending to be a warning from an anti-virus company that you are infected by the Sasser, Netsky, Bagle, Blaster or MyDoom worms. The Netsky author is preying on users' fear of computer attack," said Graham Cluley, senior technology consultant for Sophos. "The very worst thing you can do is fall for this trick by clicking on the attached file."
If run, the worm can forward itself to addresses found on the victim's computer, spreading the virus even further.
As well as claiming to be a warning about Sasser, the worm can also refer to the viruses 'NetSky.AB', 'Bagle.AB', 'Mydoom.F', and 'MSBlast.B'.
Hiden inside the code of Netsky-AC is the following text, directed towards anti-virus companies and suggesting that the Netsky author also wrote the Sasser worm:
'Hey, av firms, do you know that we have programmed the sasser virus?!?. Yeah thats true! Why do you have named it sasser? A Tip: Compare the FTP-Server code with the one from Skynet.V!!! LooL! We are the Skynet... '
"The series of Netsky worms - like Sasser - have been tremendously successful at spreading, but it's hard to be 100% certain at this stage if the same people are behind both viruses," continued Cluley.
"Everybody should practise safe computing to ensure their computers are properly defended from viruses and worms."
More information about the W32/Netsky-AC and Sasser worms can be found at: http://www.sophos.com/virusinfo/analyses/w32netskyac.html