A new variant of the Nachi worm which attempts to cleanse computers infected by MyDoom and download Microsoft security patches to unprotected computers has careened onto the Net this morning. Nachi-B (AKA Welchi) uses the same security vulnerability exploited by the Blaster worm to spread. Once it infects target machines the worm attempts to search and destroy any traces of MyDoom infection - before downloading patches for the Microsoft vulnerability it used to infect the system in the first place.

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