Hackers are spreading seven new variants of the Spamta worm.
The worm attaches itself to emails posing as delivery error messages, enticing users to click on a malicious attachment.
Creators of the worm have put numerous strains in circulation in a short period of time, increasing the probability of infecting computers. Variations to the worm include the size or compressed format of the virus files and the files copied to infected computers.
This fresh batch of worms comes just a month after the previous set of Spamta worm variants, which contained 67 versions.
Luis Corrons, director of virus research company PandaLabs, said hackers want to make home users forget to defend themselves.
"It would seem that the creators of Spamta are determined to saturate the internet with hundreds of variants, although their ultimate objective is not very clear," he said. "We believe that the strategy could be to get users and security companies so accustomed to these worms that they drop their guard, and then the creators can strike by putting far more dangerous variants in circulation."