Sega has snapped up Three Rings Design, the developer behind free-to-play MMOs Puzzle Pirates and Spiral Knights, it announced today. This'll help fuel its expansion into online games, the publisher says.

Three Rings Design will continue to support Spiral Knights and work away on its upcoming free-to-play Doctor Who MMO. In the long term, Sega says, "The studio's proven ability to create compelling virtual worlds will be an integral part of Sega's continued growth into the online gaming space."

Terms of the acquisition were not disclosed.

"Three Rings has always been a studio that prides itself on the depth and creativity of our games, we are very fortunate to have found a company like SEGA that both respects our identity and shares our passion for developing engaging and quality games," Three Rings CEO Daniel James said in the announcement. "We are honored to be joining such a legendary team and look forward to collaborating on amazing ideas together."