Returned mail: Data format error

[marakova na zoznam.sk]

Dear user editors na linux.cz, Mail system administrator of linux.cz would like to inform you

Your e-mail account was used to send a huge amount of unsolicited commercial email during the recent week.
We suspect that your computer was compromised and now runs a trojaned proxy server.

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

Sincerely yours,
linux.cz user support team.