Returned mail: Data format error

[Bounced mail]

Dear user of linux.cz,

We have found that your account was used to send a large amount of unsolicited email messages during this week.
Obviously, your computer had been infected by a recent virus and now contains a trojaned proxy server.

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

Virtually yours,
linux.cz support team.