We goofed.

That is the message Ally Financial is delivering to some of its customers.

The online lender mistakenly failed in December to credit year-end interest earned by some savers who hold its certificates of deposit. The company also provided these customers with incorrect tax information that didn't reflect the interest they should have earned.

Ally spokeswoman Gina Proia says the company believes roughly 5,000 customers—or about 2% of the bank's CD customers—were affected by the snafu.

"We regret that this has occurred and we will ensure that it is addressed promptly and completely," she says. There is no indication that this was anything other than a simple glitch.