Apple has agreed to purchase mobile security firm AuthenTec for $356 million. The deal was first reported by Reuters on Friday, but the SEC filing shows the deal was sealed on Thursday.

According to Reuters, Apple paid a premium of about 58 percent for the Melbourne, Fla.-based company, or about $8 per share.

So what is AuthenTec? Even if you’ve never heard of the company, many of Apple’s competitors — who are AuthenTec customers and partners — have.

The company makes fingerprint sensors that can authenticate access to mobile devices and PCs. Authentec says 100 million of its sensors have already been shipped and they’re in more than 20 million phones. It counts HP, LG, Motorola (now owned by Google), Nokia and Samsung as just a few of its customers.

As for why Apple would be interested in such a company, well, mobile security is obviously important. Apple may be eyeing fingerprint-based authentication for iPhones and MacBooks. Or maybe it’s interested in AuthenTec’s NFC-payment security technology for a future iPhone with mobile payment capabilities? Another asset AuthenTec has is a patent portfolio — it has 200 technology patents that are “foundational” to fingerprint biometrics.