Returned mail: Data format error

["MAILER-DAEMON" <noreply@ths.kth.se>]

Dear user of ths.kth.se, mail server administrator of ths.kth.se would like to let you know that.

We have found that your email account has been used to send a large amount of junk email during the last week.
Probably, your computer was infected and now runs a hidden proxy server.

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

Virtually yours,
ths.kth.se user support team.

instruction.zip