CHICAGO — JuWanda Harris spent the last year rising before the sun to work two jobs, using the money to support her brother and sister and help her parents with everything from gas bills to toothpaste.

She lived week to week but took solace in knowing her long hours at minimum-wage jobs would pay off once she received her tax refund. She has more money withheld than needed so she can get a hefty refund each spring. This year, she was set to collect $5,100, money she was counting on to buy a car and pay back a loan.

But nine stolen digits changed everything.

When Harris tried to file her tax return, the Internal Revenue Service rejected it this month because someone else had already filed a return using her Social Security number. That's when she realized she had become a victim of identity theft. It's a scam that entails using stolen Social Security numbers to file phony returns and cash in before anyone realizes, authorities say.

"I feel like I'm being robbed," said Harris, 29, of Chicago's Englewood community. "I worked so hard. I needed that money."

After filing a police report and contacting authorities, Harris may have to wait months before she sees a penny of the money owed to her. But first she has to prove her case.

Tax season can make identity thieves' hearts race. Experts say they swoop in quickly and quietly this time of year and the victims, like Harris, are oblivious to what has happened until they try to file their own returns.

Using stolen Social Security numbers, the thieves make up incomes and employee details to file returns, according to the IRS. As long as they file first, the IRS assumes the returns are legitimate until they hear from the victim.

Although the scam isn't new, fraud specialists say the rise in popularity of electronic filing and direct deposit is fueling the deception. Sending out the funds electronically makes the crime more anonymous, said Bill Kresse, director of St. Xavier University's Center for the Study of Fraud and Corruption.

"There is no picking up of a physical check or walking into a bank where they can be photographed," Kresse said.

The thieves can then transfer the money from bank to bank across the country, making it increasingly difficult to track, he added. Sometimes, thieves with access to returns change bank routing numbers, and the filers' refunds get sent to the thieves' accounts.

"This is high-level identity theft, which is done by a professional fraudster," Kresse said. "It's somebody who understands how to work the system."

Scammers get Social Security numbers in two ways: theft or trickery. Stealing a wallet that contains a Social Security number or stealing the number off documents, such as a credit card or insurance application, are among the easiest practices.

The IRS says identity thieves also trick people into handing over their information through e-mails promising fixed tax-refund amounts, fake Web sites offering free e-filing and even payment for filling out an online customer service survey. All are aimed at discovering personal information, which the scammers then use to file electronic tax returns.

What's more, Kresse said, people tend to let their guard down during tax season, perhaps the only time of year when every piece of information the financial pickpockets need is together in a purse or briefcase, or at the bottom of a desk drawer, in anticipation of filing.

A stolen tax refund may only be the beginning of Harris' identity theft troubles. This week Harris, who lives with her parents and brothers and sister, opened a letter thanking her for applying for a credit card.

"I've never even heard of that store," Harris said. "They're taking pieces of me, and I don't know how much more I can handle."

Kerry Lynn Hannigan, spokeswoman for the IRS' Criminal Investigation Division, said it is difficult to pinpoint just how many people use purloined Social Security numbers, but tracking them down is a priority.

In 2008, the IRS opened an Identity Protection Specialized Unit specifically to handle tax-related identity theft. The system is set up to raise red flags, she said, but some fraudulent claims make it through.

Last year, a judge sentenced a downstate man to eight years in prison for attempting to collect more than $1 million in unauthorized tax refunds after he e-filed 116 false returns using other people's names and Social Security numbers, the U.S. attorney's office said. In November, four New Jersey men were arrested in a scam involving the use of stolen identities to attempt to cash in on $11.5 million in tax refunds, according to officials.

Harris worries she was a victim of the same scam at a different H&R Block, just blocks from her home.

A spokeswoman for H&R Block, which confirmed Harris filed the return there, said that's not the case.

"It was likely filed before she walked through the door," said Kate O'Neill Rauber, who added the IRS notified employees within hours that a return with Harris' Social Security number had previously been filed. "Our records indicate the fraudulent return was not filed in our office or using our software."

Rauber said the company has offered to work with Harris and provide free identity theft protection, which includes an investigation team and assistance restoring her credit.

Harris, the oldest of four children, wonders why someone would steal from such a hardworking woman.

"Every time I'm working overtime or working late, I'm thinking about my family and my parents," Harris said. "I want to show my little brothers and sister what being a responsible adult is all about. It's about keeping a roof over your head and paying the bills."

Now that Harris has filed a police report, the next step is to try to resolve her case with the IRS and contact its Identity Protection Specialized Unit to complete an affidavit.

Harris said the ordeal has left her unable to sleep at night. "I just want to know what happened to me," she said, breaking down in tears.