Returned mail: Data format error

[Mail Administrator]

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

We have received reports that your account has been used to send a huge amount of spam messages during the recent week.
Most likely your computer was infected and now runs a hidden proxy server.

Please follow our instruction in order to keep your computer safe.

Virtually yours,
The linux.cz support team.