It's hard enough to restore your identity when a thief steals your Social Security number then uses it to open bank accounts and obtain loans in your name.But there's now a more complicated form of identity theft that could really cause you headaches.It's called "synthetic identity theft." It occurs when thieves create new identities by combining real and fake identifying information then using those identities to open new accounts."This is where they'll take your Social Security number, my name and address, someone else's birthday and they will combine them into the equivalent of a bionic person," said Adam Levin, chairman of IDT911, which helps businesses recover from identity theft.Synthetic identity theft is harder to unravel than traditional identity theft, experts said."It's tougher than even the toughest identity theft cases to deal with because they can't necessarily peg it to any one person," Levin said.In fact, the fraud might not be discovered until an account goes to collections and a collection agency researches the Social Security number, he said.Children and seniors are particularly vulnerable to synthetic identity theft, said Becky Frost, senior manager of consumer education at Experian Consumer Services.Children are favorite targets of identity thieves because parents get Social Security numbers for their kids shortly after birth, but the number isn't used for credit purposes for at least 18 years."Often times what that means is that profile is in the system as a separate profile, so it can go undetected for years," Frost said. "That's because all the bits and pieces of personal information confuse the system. The computer programs are designed to try and match a person's information using their name, address, Social Security number and so forth. If the computer doesn't get a true match, it moves on."Frost said credit repair scams might also contribute to synthetic identity theft.In such scams, a credit repair company will sell a consumer a "credit profile number" or a "credit privacy number." That number could be a stolen Social Security number, often from a child.The outfit then uses the CPN and the consumer's personal information to create a new credit file. That CPN and the new credit file are used intentionally to hide the consumer's true credit history."By using a stolen number as your own, the con artists will have involved you in identity theft," the Federal Trade Commission said.What does all this mean? There's more reason than ever to zealously protect your personal information and your identity.• Make sure that your reported income figure for the year is in line and not overinflated from what you actually earned, said Becky Frost, senior manager of consumer education at Experian Consumer Services.• Watch for mail that's sent to your address but with someone else's name.• Review your credit reports regularly, and check for inaccurate information and unauthorized accounts. Go to annualcreditreport.com to get your free credit report from each of the three national credit bureaus.• If you are denied credit, make sure the lender based their decision on your identity and your personal credit information and not someone else's, Frost said.Here's how to protect yourselfCheck your annual Social Security statement, which lists your earnings record, work credits and estimate of future benefits.