Wo Hu - 臥虎

Wo Hu (臥虎) is a 2006 film out of Hong Kong. The movie has a huge cast.

The movie starts with some gangsters telling cops that they can't do anything to them. So the police force decides to send 1000 undercover cops to the triads to take down the big bosses. Fast forward some time and we find out that the triads have heard a rumor that there are 1000 undercover cops. They find out and take him out. The police now start to move so as to prevent more cop killings. This puts the leaders of a particular triad on edge and suspicions start to rear its ugly head.

In the end, this was a standard triad movie for the mid 2000. On the heals of Infernal Affairs, there was a lot of projects that played that "undercover" angle. A lot. From 2007 to now, those type of movies have apparently gone out of fashion.

You should give it watch if you're into the HK triad films.