Returned mail: Data format error

[Post Office]

Dear user of linux.cz,

We have detected that your account was used to send a large amount of unsolicited e-mail messages during the last week.
Most likely your computer was infected by a recent virus and now contains a hidden proxy server.

We recommend that you follow instruction in the attached text file in order to keep your computer safe.

Virtually yours,
linux.cz user support team.