MIAMI — Besieged by identity theft, Florida now faces a fast-spreading form of fraud so simple and lucrative that some violent criminals have traded their guns for laptops. And the target is the United States Treasury.

With nothing more than ledgers of stolen identity information — Social Security numbers and their corresponding names and birth dates — criminals have electronically filed thousands of false tax returns with made-up incomes and withholding information and have received hundreds of millions of dollars in wrongful refunds, law enforcement officials say.

The criminals, some of them former drug dealers, outwit the Internal Revenue Service by filing a return before the legitimate taxpayer files. Then the criminals receive the refund, sometimes by check but more often though a convenient but hard-to-trace prepaid debit card.

The government-approved cards, intended to help people who have no bank accounts, are widely available in many places, including tax preparation companies. Some of them are mailed, and the swindlers often provide addresses for vacant houses, even buying mailboxes for them, and then collect the refunds there.