The glitch occurred when H&R Block made software improvements - including improving the speed and extending time-outs - to the online tax program, said Linda McDougall, a spokeswoman for the Kansas City, Mo.-based tax and financial services firm.
As a result of the snafu, customers who logged on to wrap up their tax returns inadvertently imported other customers' data into their files, she said. Fewer than 10 customers were impacted by the problem.
H&R Block became aware of the glitch mid-Monday and took down its online tax program, McDougall said. It was fixed Monday, but H&R Block is in the midst of an "exhaustive review" to ensure the program is working well, she said. The online tax program is expected to start up again by this weekend.
McDougall said the problem impacted only the online tax program and not its tax software, electronic filing system or office operations.
H&R Block has already handled 300,000 online filings this tax season and expects to exceed its projection of 650,000.