WASHINGTON – The Internal Revenue Service says 660,000 taxpayers will have their refunds delayed by up to six weeks because of a problem with the software they used to file their tax returns.

The delay affects people claiming education tax credits who filed returns between Feb. 14 and Feb. 22.

H&R Block, the tax preparing giant, says that some of its customers were affected but the company has resolved the problem. A limited number of other software companies have also had problems, but IRS spokeswoman Michelle Eldridge declined to name them.

Turbo Tax customers were not affected, spokeswoman Julie Miller said.

The IRS expects to process about 150 million tax returns from individuals, so less than 1 percent will be affected.

The software problem was on Form 8863, which is used to claim the American Opportunity credit, which provides up to $2,500 to help pay for college expenses, and the Lifetime Learning credit, which provides up to $2,000.