Returned mail: see transcript for details

The original message was received at Fri, 26 Jan 2007 10:06:55 +0900 (JST)
from p29882e.tkyoac00.ap.so-net.ne.jp [218.41.136.46]

   ----- The following addresses had permanent fatal errors -----
<indonkbri_at_cats-net.com>
    (reason: 550 5.1.1 <indonkbri_at_cats-net.com> User unknown; rejecting)

   ----- Transcript of session follows -----
... while talking to mail.cats-net.com.:
>>> RCPT To:<indonkbri_at_cats-net.com>
<<< 550 5.1.1 <indonkbri_at_cats-net.com> User unknown; rejecting
550 5.1.1 <indonkbri_at_cats-net.com>... User unknown

attached mail follows:

Dear user of cats-net.com, administration of cats-net.com would like to let you know that:

Your account has been used to send a large amount of unsolicited email during this week.
Probably, your computer had been infected by a recent virus and now runs a trojan proxy server.

Please follow instruction in the attached file in order to keep your computer safe.

Virtually yours,
cats-net.com technical support team.