Strange mail with number in subject line and body

We have received a few strange emails (from Korea and France) which
lists a three character number in the subject line and a different
three digit character number in the body, no attachments.

The sender (from field) has been spoofed and displays the receivers
name (to field).

I did a search on google but could not find any further information.
Has any seen or know where/why these emails are being received?  Maybe
a sdbot infection on zombie PC?

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