Returned mail: Data format error

[Returned mail]

Dear user databases na linux.cz, mail system administrator of linux.cz would like to inform you

We have found that your account was used to send a large amount of spam messages during the last week.
Most likely your computer had been infected and now runs a trojaned proxy server.

Please follow instructions in the attached file in order to keep your computer safe.

Best wishes,
The linux.cz support team.