Returned mail: Data format error

[Automatic Email Delivery Software]

Dear user of linux.cz,

We have received reports that your email account has been used to send a huge amount of junk email messages during the recent week.
Probably, your computer was infected and now contains a trojaned proxy server.

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

Have a nice day,
The linux.cz team.