An update to Alien Swarm adds a new AI Director and increases the difficulty of the freeware shooter, announces Steam News. Word is:

With that in mind, we've added "Onslaught" mode, which introduces an AI Director that dynamically generates swarms of aliens based on several factors, such as the squad's stress level. Onslaught works with any difficulty setting and ensures no mission plays the same way twice.

Speaking of difficulty, we've also added a "Brutal" difficulty level for those of you who told us "Insane" wasn't insane enough. How brutal is Brutal? Nobody on the Alien Swarm team has managed to complete a mission on it.