Researchers are reporting a new worm in the wild that overwrites master boot records (MBRs) of all available drives with its own data, making the data stored on a user’s computer inaccessible.

Restoring the corrupted data is complicated, requiring specialized software or a third-party service provider, the researchers say.

Win32/Zimuse A and Win32/Zimuse B has been spotted on hundreds of computers, according to security service provider ESET. Immediately after the outbreak, only users in Slovakia were affected, accounting for more than 90 percent of all infections. Now, however, the greatest number of infected computers is in the United States, followed by Slovakia, Thailand, and Spain, ESET says.

The worm spreads in two ways, according to ESET. It could be embedded in legitimate Websites in the form of a self-unpacking ZIP file or an IQ test program, or it could be spread via portable media, such as a USB device. Its ability to spread via portable media could allow the worm to spread faster, the researchers say.

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