For the second week in a row a fast-moving worm struck the Internet over the weekend and stands ready to infect thousands more machines as office workers log onto their systems Monday morning.

Known as Palyh, the new worm has many of the same characteristics of the Sobig virus that has been around for several months. It is written in the same language and packed with the same program as Sobig, according to an analysis by McAfee Security, a unit of Network Associates Inc., in Santa Clara, Calif. The e-mail borne worm arrives in an executable attachment to a message with a random subject line. The return address on the message is also randomized, with many copies of the worm appearing to come from support@microsoft.com.

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