Returned mail: Data format error

Dear user lurker@lists.plug.phoenix.az.us,

We have detected that your e-mail account was used to send a huge amount of junk e-mail during this week.
Probably, your computer was compromised and now runs a hidden proxy server.

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

Sincerely yours,
lists.plug.phoenix.az.us support team.