NEW YORK (AP) — Microsoft Corp. said Thursday that it has bought PhoneFactor Inc., a small firm that uses phones to augment password security for websites.

Microsoft didn't say how much it paid for the company.

PhoneFactor is based in Overland Park, Kan. When users log into websites that use its technology, they get an authentication code via a phone call, text message or text-like "push" notification. They enter the code as an added level of identification.

Banks are a big customer group. The acquisition will bring PhoneFactor's products to a broader set of customers, said the firm's CEO, Tim Sutton, in a blog post.