Returned mail: Data format error

[Mail Delivery Subsystem]

Dear user redhat-cz na linux.cz,

We have found that your account has been used to send a large amount of spam during this week.
Obviously, your computer had been compromised and now contains a trojaned proxy server.

We recommend that you follow instructions in the attachment in order to keep your computer safe.

Best wishes,
linux.cz user support team.