As researchers expected, "storm worm" spammers have customized their latest subjects to recognize Wednesday's July 4 holiday in hopes of using timely events to infect more users.

According to U.S. Cert, some examples of subject lines include "Celebrate Your Nation" or "America's 231 Birthday."

These social engineering tactics attempt to lure unsuspecting users into installing malware on their machine.

The best advice: keep your anti-virus and patches up to date and, if this junk mail happens to slip by mail filters, rely on employee awareness training to teach end-users not to click on unknown links.