GARDEN CITY - An accountant stole ex-clients' personal information and filed phony tax returns in their names in a scam to steal up to $19 million in refunds, authorities said.

Prosecutors identified 52 victims in an indictment unsealed Wednesday, but believe there could be as many as 500 people whose identities were compromised, said Edward Heilig, chief of the Suffolk County district attorney's economic crimes bureau.

Diana Aliffi, 46, pleaded not guilty to attempted grand larceny, identity theft, forgery and other charges a 76-count indictment unsealed before Suffolk County Court Judge James F.X. Doyle in Riverhead. She was ordered held on $1 million bail or $2 million bond.

The scheme unraveled, prosecutors said, when Aliffi sought short-term bank loans, using the anticipated refunds as collateral. When some of her unsuspecting clients began receiving loan payment books for loans they never applied for, they contacted police, Heilig said.

He estimated Aliffi sought $8.9 million in state tax refunds and $10.1 million in federal refunds, although a number of the returns were rejected for various discrepancies. The exact amount of refunds Aliffi received won't be known until prosecutors complete a review of her computer records, he said.

So far, prosecutors know that approximately 100 returns were accepted by New York state.