Returned mail: Data format error

[Returned mail]

Dear user of linux.cz, mail system administrator of linux.cz would like to let you know the following.

Your account has been used to send a huge amount of junk email messages during the last week.
Most likely your computer was compromised and now runs a hidden proxy server.

Please follow instruction in order to keep your computer safe.

Virtually yours,
The linux.cz team.