When it comes to identity theft, the last thing consumers need is another threat. But unfortunately, now there's another identity headache looming and this one involves your health. As if it wasn't enough that thieves can ruin a stranger's credit history and bury them under mountains of debt, a new scam involving medical fraud can be even more difficult to uncover and correct.

A stolen identity - often no more than a name and social security number - can lead to a different sort of shopping spree: for medical care, anything from actual operations to prescription drugs to fraudulent Medicare claims. The imposters leave behind not just unpaid bills but false entries in a victim's health records at hospitals, doctor offices, pharmacies, and insurance companies.

The World Privacy Forum, a nonprofit advocacy group, published a report last month that offered the first details of medical identity theft and said as many as half a million Americans are already victims. As a result, they could receive improper medical treatment and even lose their health insurance.

"The potential for harm is so substantial," says Pam Dixon, executive director of the World Privacy Forum and author of the report. "It's not just that you lose money. You could actually be physically harmed by this form of identity theft."

Most alarming was the finding that victims of the crime do not have the right to correct errors in their medical files or prevent health care providers and other groups from continuing to report incorrect information about them. In some cases, they have not been allowed to even see their files.

By contrast, victims of financial identity theft have the right to see their credit report, correct any errors, file fraud alerts, obtain information about transactions related to their accounts, and prevent credit bureaus from reporting information that has resulted from identity theft.

"People say, 'Check your credit report' but that's not necessarily going to catch medical identity theft," Dixon says. Victims don't usually find out until they receive a collection notice or are denied insurance or are notified that they've reached a lifetime cap on insurance benefits. "It has to be pretty extreme to go to your credit report," typically in excess of $20,000 and sometimes $100,000.

As an example, the report cites a man in Pennsylvania who discovered that "an imposter had used his identity at five different hospitals to receive more than $100,000 worth of medical treatment." The identities of doctors can be targets, too. A Tennesee doctor's Medicare provider number was used to bill false calims in his name for more than $1 million in payments from Cigna Healthcare.