In my opinion, the best way to keep clean of spam is simple: The first rule is NEVER reply to spam, NEVER click the unsubscribe link and NEVER e-mail to the unsubscribe address.
Scope Some idiot created a SSH worm that uses a dictionary attack to try to log into a computer over port 22. The worm tries to set up shop on your computer and tries to find the next vulnerable computer. This clogs up networks with bazillions of SSH login attempts.