If you drive a used car, do you really know how safe it is?

It turns out thousands of cars are on the road right now that pose a deadly threat to their owners and other drivers.

This is a widespread problem, and sometimes it turns deadly: Cars that have been totaled and have weak frames. Sometimes, they are put back on the road illegally.

Terry Dunscheski paid nearly $20,000 for one Toyota SUV. When he took it to his mechanic, he was shocked to learn he'd been driving his family around in a re-built wreck.

MORE ON THIS STORY Washington Department of Licensing Used Car Complaint Numbers: Olympia office and Western Region Headquarters: (360) 664-6475 Seattle office: (206) 706-4255 Department of Licensing Web site: http://www.wa.gov/dol Information about purchasing a vehicle Check to see if a dealer is licensed Get a vehicle history report: http://www.carfax.com How To Avoid Buying A Rebuilt Wrecked Car From the General Services Administration

"Right here, you can see where they cut and spliced another top off another wreck onto it," he said.

This is what the Dunscheski's car looked like before someone secretly patched it back together and sold it.

"It had been re-welded where it was not even safe to drive," Dunscheski said.

Unfortunately, the Dunscheskis are not alone.

"There are literally thousands of cars out on the road today that have damaged frames and consumers are unknowingly driving them, putting themselves and their families at risk," said Larry Gamache of Carfax.com. "The only way to protect yourself from a damaged frame is by getting a mechanic to inspect it."

Some body repair shops used outdated methods to repair car frames. But now there are state-of-the-art systems such as "Auto Scan," which use lasers to check the frame's specifications to within one millimeter.

"As little as eight millimeters is the difference between a safe vehicle and an unsafe vehicle in terms of protecting you and your family in the event of an accident," said Randy Gard, an auto repair expert.

Traffic safety experts say a car's frame is even more important to your safety than seat belts and airbags if you get in a crash.

"It's the single greatest safety factor in a vehicle today. If the frame is not repaired correctly, the other safety systems may not function properly," Gard said.

"Get that car into your mechanic, get them to inspect the frame, make sure there's no prior damage you didn't know about."

"Believe me, it is nice to be able to sleep at night, knowing that you are in a safe vehicle," said Dunscheski.

It's also a good idea to check the repair history of any used car you plan to buy. You can do that by asking the seller for the car's service records, or doing a bit of research online.