CENTREVILLE, Va. --- A new study by Carfax shows that millions of cars severely damaged in major accidents have been rebuilt and are up for sale.

Over the past five years, the number of salvaged cars revealed by Carfax Vehicle History Reports has increased nationwide by more than 50 percent.

"This problem is more widespread than we previously thought," said Larry Gamache, communications director at Carfax. "Based on our data, the number one concern consumers should have right now, even above flood damage, is unknowingly buying a used car that was badly damaged in an accident. Buying a salvaged car may not be a bad investment, but you must make sure you are aware of any prior damage and, more importantly, see that the proper repairs were made. Checking the information gathered in our database is the first step consumers should take to protect themselves from unwanted problems."

Experts estimate that more than 5 million cars annually are deemed salvage after severe accidents. More than half of these cars are resold, many by sellers who intentionally hide their damaged past from unknowing consumers.

Some of the common problems associated with previously wrecked vehicles may include:

** Title washing --- Title documents may be altered to remove a salvage brand and obtain a clear title from another state.

** Air bag fraud --- Scam artists are known to replace deployed air bags with phony or non-working air bags to cut costs.

** Structure/frame damage --- As little as 8mm can compromise a car's structural integrity, which also may affect many of the car's safety features.

** Odometer rollbacks --- The odometer also may be rolled back to further inflate the perceived value of the vehicle.

** Car clipping --- Some rebuilt wrecks are actually two different cars welded together.

Forecasters predict slower car sales this year, but still more than 40 million used cars are expected to be purchased.

"The used car market is a target-rich environment for scam artists," added Gamache. "Many salvage vehicles are rebuilt properly and will run safely again. However, con men alter title documents and make cheap cosmetic repairs to others so they look as good as new on paper and in person. We urge anyone buying a used car to get a Carfax Vehicle History Report that qualifies for the Carfax Buyback Guarantee and have a mechanic thoroughly inspect the vehicle prior to purchase."