The FTC study, which was based on 4917 telephone interviews conducted between 27 March and 11 June 2006, indicates that 3.7% of all American adults were victims of ID theft in 2005. This is below the 4.6% rate recorded in the FTC's 2003 poll, but the agency says the decline is "not statistically significant".

Estimated total losses from ID theft came in at $15.6 billion - considerably lower than the estimate of $47.6 billion in the 2003 survey. This reflects lower estimates of both the prevalence of ID theft and the average loss per incident. But the FTC says some of these differences result from the changes in survey methodology.

"Thus, we cannot determine whether total losses have actually dropped significantly between 2003 and 2006," says the report.

Of the victims, around 3.2 million, or 1.4% of all adults, experienced misuse of existing credit card accounts, while 3.3 million, or 1.5%, experienced misuse of non-credit card accounts. Around 1.8 million victims, or 0.8%, found that new accounts were opened or other frauds were committed using their personal information.

Over half - 56% - of victims don't know how thieves obtained their information. Just one per cent say it was the result of hacking into a computer and another one per cent blamed phishing.

The FTC says in more than half of the incidents victims incurred no out-of-pocket expenses as a result of ID theft. Some victims, however, incurred substantial expenses, with 10% of all victims reporting costs of $1200 or more.

Around 37% of victims reported other difficulties, including harassment by debt collectors, the denial of new credit or loans, disconnection of utilities and problems obtaining or accessing bank accounts.

ID theft is also time consuming for victims with an average of four hours being spent resolving problems and five per cent of people taking at least 130 hours.

The survey found that fraudsters obtained more goods and services - and victims spent more time and money recovering - in cases where the thief opened new accounts rather than only hijacking existing accounts. Where the theft was limited to the misuse of existing accounts, the median value of goods and services obtained by the thieves was less than $500. Where the thieves opened new accounts or committed other frauds, the median value of goods and services obtained was $1350.

Lydia Parnes, director of the FTC's Bureau of Consumer Protection, says it is important that people learn how to deter identity thieves, detect suspicious activity on financial records and defend against the crime.

"Consumers have great tools at their disposal in their fight against identity thieves," says Parnes. "For example, the law gives every consumer the right to get their credit report for free once every 12 months from each of the three national credit reporting companies. Monitoring your credit report periodically is one valuable way to check for activity that you didn't authorise."

However the Consumers Union in the US says the FTC's report underscores the need to provide consumers with stronger protections against ID fraud.

"Identity theft is a huge headache that continues to plague millions of Americans every year," says Gail Hillebrand, director of the consumer group's Financial Privacy Now campaign. "It's time to require businesses and government agencies to safeguard sensitive personal data and to give consumers the protection they need."

Read the FTC's ID Theft survey report here: