Sir Richard Branson of Virgin fame announced via his Twitter feed that he's investing in mobile payment start-up Square.

According to a post on the Virgin corporate site, Branson "took interest in Square's rapid growth and novel technology, in particular its free hardware that allows anyone to accept credit card payments anywhere, anytime."

"I’m very passionate about helping people start and grow successful businesses, and Square is an incredible technology that inspires and empowers everyone to be an entrepreneur," Branson said.

Specifics on the amount invested were not released, but Reuters is reporting a Square spokeswoman said it was a "multimillion dollar" investment. The spokeswoman also told Reuters it was a "personal investment."

Square recently announced a $100 million round of Series C funding led by Kleiner Perkins Caufield and Byers.

Square is known best for its mobile point of sale device that turns any smartphone into a credit card reader, allowing small businesses to process credit and debit transactions.

The company also has a mobile wallet product, the Square Card Case, that was in the news last week thanks to some interesting updates that allow users to make purchases at the point of sale based on proximity to a merchant. 

For more on this subject, please visit the POS research center.