Alert level 4 is pretty damn high. You must have been one bad robot.
I'm considering making the security level and purge amounts more obvious. I started with an intentionally semi-opaque system. Purge lowers total security value by 200 each time, and Alert Level 4 is anything over 1600. (Right now the threshold for each level is double that of the previous level.)
Overall there's also a need to tweak how threat values are accumulated, but it was necessary to see how you all fare in certain situations before making any meaningful changes. It's a pretty central component for the whole experience. Too low and the entire game would be too easy; too high and the chances of getting roflstomped are pretty high unless you're extremely careful about threat management.
The problem with doing too much tweaking now is that later more branches will be added, and leaving the main complex for a branch is an easy way to lower your threat (by taking a "sideways" detour), so you'll have very significant new options for staying alive.
