WASHINGTON (AP) – 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.