The "Happy New Year" worm took the top spot in December's list of most prevalent malware, Sophos reported Wednesday, unseating former leaders such as Stration and Netsky.

Sophos calls the worm packaged with the heavily-spammed "Happy New Year" malicious e-mail a variant of the "Dref" family, although other anti-virus vendors have slapped their own names on the malware. Symantec, for example, calls it "Mixor.q," while Kaspersky Lab dubs it "Tibs."

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