First Chicago NBD Corp. almost gave away the bank last week.

More than 800 customers each received an extra $924.8 million in their checking accounts - because of a computer programming error. The windfalls, however, proved short-lived as the bank's technicians sprang into action.

"Our controls worked very well," said James Lancaster, executive vice president in charge of Illinois retail banking. "We caught it quickly. But every time something like this happens, we go back and figure how it happened."

The glitch, at the company's First National Bank of Chicago unit, was discovered at about 4 p.m. Thursday after two customers reported the error. Bank employees eliminated the amounts erroneously deposited or froze those portions of the accounts.

By noon Friday, no customer was able to access any of the money deposited by error, said Mr. Lancaster. He said the bank believes that none of the customers affected by the glitch withdrew money that didn't belong to them.

Though such incidents are rare, this is not the first time a bank has been embarrassed by a computer error.

In February 1994, Chemical Banking Corp. incorrectly debited a total of $15 million from 100,000 customer accounts. As a result of the mistake, some customers were denied cash, while others had checks bounce.

A month later, Chemical discovered a computer error charged 20,000 small-business customers erroneous service fees. The bank apologized for the errors through letters to customers.

Some employees at First Chicago worked through Saturday to make certain all accounts were purged of the mistaken credits. Mr. Lancaster refused to reveal the details of the snafu, saying that the bank had little to gain by such a public explanation. But he added that bank technicians were working to make sure that it never happens again.

Mr. Lancaster said the only expense to the bank will be the overtime paid to employees who worked after hours to isolate the problem. He said he's also reviewing how the individual committed the error. "The real question is whether the programmer followed all the procedures," he said.

The $924.8 million figure was generated by the computer, but Mr. Lancaster said that number doesn't correspond with any customer account. In fact, the total amount accidentally deposited - in excess of $740 billion - is more than six times the bank's asset total.

While First Chicago has discovered small mistakes in balances in the past, there had never been anything of such magnitude. "If this was $1,000 credited to somebody's account, this wouldn't be news," he said.

First Chicago hasn't decided whether its going to contact customers. "We're still working on that one," said First Chicago spokesman Thomas Kelly. "Many of the customers didn't even know."

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