“A worm that first disguised itself as an e-mail from computer vendors is now attempting to trick MSN Messenger users into executing malicious files.

The Chod.B worm, which was first discovered on April Fools’ Day, spreads via e-mail purportedly from Microsoft and security companies Symantec and Trend Micro.

When using the MSN Messenger instant-messaging client as its propagation tool, the virus sends out messages to contacts from the infected user’s address book, warning them that they are about to receive a file. The virus then sends a file designed to infect the recipient’s system.

Adam Biviano, Trend Micro’s senior systems engineer, said the development is “alarming” because the technique mimics the behavior of a real IM user.

“The virus will send you a message first saying, ‘Check out what I just found on the Internet,’ and then sends you (the malicious) file. It is not just sending files out of the blue anymore–it is trying to imitate what a friend in your contact list would do,” he said.”

[Continue reading E-mail worm graduates to IM]