I encourage people to inspect blhack so you know what to look for on your server. I would look up some vids on youtube to see what kind of stuff it can do, it makes it very easy to spot it on your server.
You can actually detect freezing just with Torquescript.
Do three checks.
1) Has the player moved?
2) If the player hasn't moved, do they have a velocity other than 0?
3) If the player isn't moving, but has a velocity, start checking their Ping.
If the player isn't moving, has a velocity, and their ping is changing, then they're using a freeze hack.
Though, if anyone's going to write a script to prevent this, do note that:
The moment a player starts to lag, this could get triggered. Best to see if it happens across multiple ticks.
While very, very unlikely, a player could end up at the same position as their last tick. Could be caused by spam fetching/finding. Should reset the 'number of ticks the player was frozen' each time the player is teleported.