Christine O'Neill had been working in the cafeteria of the King Philip Middle School in Norfolk for three weeks when she was called to the superintendent's office. She was told her criminal background check had come back, and she was fired.

O'Neill left, sat in her car, and wept -- not because her past had come back to haunt her, but because someone else's had.

O'Neill, 48, of Medway, did not have a criminal record, but her identity was intertwined with that of a petty criminal who had stolen O'Neill's license in the 1980s. When the woman was arrested, she gave the license to police, making O'Neill one of her aliases.

As a result, the woman's 10-page rap sheet -- known in Massachusetts as a Criminal Offender Record Information, or CORI -- was kicked back last fall when the school did a background check after O'Neill applied for the job.

"I didn't do what she did. It shouldn't even matter what she did," O'Neill said of the woman who stole her license. "It's not me, and that's what I don't understand: Why can't they fix it? What's the big deal?"

Massachusetts created the CORI in 1972 so law enforcement officials -- such as police, judges, probation officers and prison wardens -- would have quick, easy access to criminal records.

Since then, the state has made criminal background checks mandatory for many jobs, such as those that involve working with the elderly, children or disabled people. Checks can be made for people applying to get into public housing, and private landlords and employers use background checks to screen applicants.

In 1993, there were 2,000 entities in Massachusetts certified to ask for CORIs from the state. These days, there are about 10,000.

The state's Criminal History Systems Board, which oversees the CORI system, received nearly 1.5 million requests for information last year, more than triple the number requested in 1998, according to a recent report from the Crime & Justice Institute and the Boston Foundation.

Thirty-seven states allow employers and licensing agencies to consider an applicant's arrest record, and 33 states do not permit convictions to be sealed, according to a report last year from the Legal Action Center in New York.

The report, overall, gave Massachusetts' CORI system high marks for, among other things, allowing first-time felony records to be sealed after 15 years and forbidding employers from asking about arrests that never led to conviction. But the state lost points in other areas, such as allowing employers to refuse to hire someone with a criminal record.

Most states also allow local housing authorities to consider convictions when picking tenants, and 27 states allow arrests to be considered, according to the report.

The number of people affected nationally is huge. Some 630,000 people get out of state and federal prisons each year with criminal records. According to the U.S. Department of Justice, in 2003 almost 30 percent of adult Americans had a state criminal arrest record.

Helping to fuel the surge is the growing business of selling personal information. There are more than 400 companies selling criminal histories and other information over the Internet, according to Debbie A. Mukamal, director of the Prison Re-entry Institute at the John Jay College of Criminal Justice in New York, and the author of the Legal Action Center report.

There is little disagreement that there must be access to criminal backgrounds to protect the innocent and prevent people with criminal histories from hiding their pasts. But as rap sheets become open books, they can haunt people.

Today, Christine O'Neill carries a letter from Wrentham District Court saying her identity had been stolen, but her name is still on the other woman's CORI, according to her attorney, Francisca Fajana, of the Massachusetts Law Reform Institute, a legal services organization.

"That's a huge, huge impact. You can't get a job, you can't pay your rent, can't put food on the table," Fajana said.

Cheryl Murphy, 35, did not understand why employers were rejecting her job applications until she begged one to tell her. The employer pointed to Murphy's six-page CORI of dismissed charges, dating to 1986, when she was a teenager arrested for sleeping under a tree on Martha's Vineyard.

Because she cannot get a regular job, Murphy works five days a week on the overnight shift for a Boston homeless shelter, and double shifts as a weekend waitress at a restaurant.

"I've been given a life sentence, and I've never been convicted of a misdemeanor," she said. "CORIs carry more weight than the best of resumes."

State regulations that went into effect in June require agencies seeking CORI reports to ensure they have the right person by asking for information such as mother's maiden name and physical attributes. Social Security numbers are optional.

The new regulations also give people new rights to dispute the information on a CORI report, and create safeguards to prevent dissemination of the information. But critics say a bigger fix is needed for what they say is a problem with easy access to criminal records.

Unlike other states, Massachusetts does not use fingerprints to match the names on CORIs with the people who actually have the record. The state's Criminal History Systems Board is working to remedy that by creating new identity fraud protections, said Curtis M. Wood, the board's deputy director.