Private equity firm Thoma Bravo, which has offices in both San Francisco and Chicago, said this morning that it has acquired Crossbeam Systems, a developer of network security products. Financial terms of the buy were not disclosed. Crossbeam is based in Boxborough, Mass., and has more than 200 employees. The two said that Crossbeam's management with will work Thoma Bravo to accelerate its growth. Crossbeam was venture backed by Charles River Ventures, Commonwealth Capital, Focus Ventures, Intel Capital, Matrix Partners, North Bridge Venture Partners, and Tudor Ventures.