The tipoff with these emails is that they have (No Subject) in the subject line. Opening the email should be safe enough, but there will always be a link in the email, and you DO NOT want to click on that. It could be a virus, or it could be spam. You don't want to find out which.
Run a malware killer weekly...mine is "Super Anti-Spyware Free Edition". It seems to work well. The quick scan is generally good enough. Sometimes I'll run the full meal deal and it never finds anything beyond what the quick scan did. It will ask to do updates occasionally...I let it. My computer guru recommended it.

Steve