Oh for Christ's sake there IS NO TRUE DATA SECURITY IF YOU HAVE PHYSICAL ACCESS TO A MACHINE.
Go ahead, encrypt your files, password protect them, depend on Windows *laff* to keep them safe. Whatever, if someone needs/wants to get them, has the know how, and has physical access to the machine there IS NO SECURITY. Period. End of story.
As for erasing data. Impossible. There is NO WAY to eradicate teh data on the magnetic platters in a hard drive. Sure you can garble it nicely by rewriting over it until time runs out, but it's not completely gone, and with enough time (and effort, though practicality DOES kick in at some point) the information can be recovered. The only REAL way to destroy the information is to melt down the disks (and/or otherwise physically destroy them).
As for the images coming in through 'spam e-mails'.... suuuuuuuuuuuuuuuuuuuuuure....
Guess what? All that stuff goes to STANDARD FOLDERS. Your computer holds it's temporary files in SET PLACES. They're called "Environment Variables".
I threw that in to silence all you "But my temp files don't go to the default places!". Bottom line is, if it's a TEMP file, that is EASY to find out. And where the file came from... IS EASY to find out. This is why computer crime is SO EASY to prosecute. There IS a trail, and it's tough as all get out to erase your tracks. Even if you know what you're doing, if you've got something to hide, you'd better develop a hightened sense of awareness (paranoia) or you're going to get nailed faster than you can say "The virus did it!".
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie.Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")