SEATTLE -- We've all gotten pretty good at guarding against identity theft.

We shred our documents and protect our pin numbers and Social Security numbers.

But there's a threat many people don't think about. And it comes from a common machine you might have at home.

We found an old fax machine found sitting on a shelf at a local thrift store. It cost just $7.

If we were crooks on the prowl, we'd now have a wealth of private information. Because every document this machine has ever received is perfectly preserved on a carbon ribbon, from birth certificates, credit card receipts and medical and dental records to legal documents and banking information.

The Problem Solvers discovered these carbon rolls are routinely tossed in to recycle bins. Old machines are abandoned at second-hand stores with the ribbons still inside. Some times, they're recycled at Ron Berger's print shop.

"It's a huge scare that people are not aware of," said Berger. "Schools, doctors, dentists, rental places -- the sky's the limit."

The scare comes from thermal fax machines -- an inexpensive old-school fax still on store shelves and used in thousands of homes and offices.

Each fax roll contains between 250 and 500 feet of carbon paper. That's yards and yards and yards of private, personal information.

Jerry and Mary Lane had no clue a perfect copy of one of their checks was still on a carbon roll their dentist had tossed in a recycle bin.

"Not a good situation," said Jerry Lane. "It's very legible. Someone could probably even use that to make checks."

"I don't like having my information out there," Mary Lane said. "That is troubling."

We showed Howard Schmidt, former head of security for Microsoft, what we found.

"Criminals will look for this sort of thing. Not only the bank information, the social security number, but also the signature because that will give them a lot better credibility when they try to forge something," he said.

And it's even better if an identity thief can get his hands on a birth certificate.

Bruce Becker was shocked when we showed him a pristine copy of his young son's birth certificate. A copy of the document and a registration form with all the family's personal information was left inside a fax machine that a little league coach recycled.

"With technology today, they could do a lot of things with that. It's kind of disturbing," he said. "These things are pretty scary when you start to think of the kids involved here and all the personal information on these children here."

Schmidt says predators might use this personal information to track and befriend a child. And thieves will sit on the child's birth certificate until he's 18, waiting to apply for credit.

"Criminals will store this stuff. This stuff doesn't have a life span on the Internet. It doesn't die; it's there forever," he said.

And it all could have been avoided if the machine's owners had been informed.

What we haven't told you yet is these carbon rolls are not recyclable; they should never be tossed in a recycle bin.

The only way to destroy the information is to crinkle the carbon paper or to incinerate it.

Bruce Becker is just glad to get his son's information back. And so are the Lanes.

"These fax rolls are secure documents. They should be treated as secure documents and be destroyed," said Berger.

So the next time you send a fax, know where it's going and what kind of machine it's going to.

You should be cautious with fax machines and even printers that have memory.

If you don't wipe the memory clean before you recycle or sell it, someone could print out everything you've received or printed on your machine.