Delete it.
It's most likely that someone you don't even know has
a virus that sends out malicious emails using addresses
in the infected computers files.
They may be somebody on Tweeters who doesn't even
know this is happening from their computer.

Also I tell all my friends and relatives to never send an
email with no subject line for the same reason as above.
We've got no way to verify that it's really from them,
and if it has an attachment, it's almost surely bad news.

Good luck.