And your co-workers think you're paranoid. Until their email is hacked, or they fall for a phishing scheme, or worse. Which, of course, doesn't make you feel any better.

Still, we soldier on in our imperfect, insecure digital existence: making sure we change default passwords on equipment, use strong passwords, never click on links embedded in emails, etc etc. But when it comes to computer security, we must forever educate ourselves on malware. Threats continually evolve, and eternal vigilance is the price of data protection.

So here's something I didn't know and you likely didn't either--from an IDG News Service story by tech journalist Robert McMillan, quoting independent computer forensics expert Frank McClain: "Because flash memory cells stop working after they've been overwritten too many times, flash devices use tricks called 'wear leveling' to even out how the memory cells are used. A side effect of wear leveling is that it is 'almost impossible' to completely erase data from a flash device."