Forgive my ignorance, but my basic google-fu did not pull up an answer. I lived in China for a few years and I thought it was the Public Security Bureau, but it looks like they do a different kind of service.
Do they have a CIA or KGB kind of agency? What is it called? What do we know about it?
In addition to the MSS, the Second (HUMINT),Third (SIGINT), and Fourth (ELINT) Departments of the PLA engage in military intelligence.
The Ministry of Public Security used to engage in secret police work, monitoring of dissidents, etc., but since the 1980s, that duty was turned over to MSS. The Ministry of Public Security is responsible for monitoring the internet, though.