In explaining why the Half-Life 2 source leak is so damaging (apart from the potential theft of Valve's IP), some helpful people on slashdot explain how unscrupulous (or just plain teenage) players might exploit the code to cheat. In particular, one poster mentions some of the Starseige:Tribes cheats floating around:
For instance, in Starsiege:Tribes, since the rendering engine has been successfully hacked, people have been able to write some clever and EXTREMELY extensive cheats -- you can customize the visibility of the terrain, of individual objects (like buildings -- make them partially transparent to see people around corners), remove fog from maps, have pointers to the person with the flag, and most infamously, change the model for the flag into a twenty-story-tall red and green stick figure with a gigantic smiley face. This cheat is known as 'Happy Flag', and it makes it pretty much impossible to confuse the enemy team as to the location of your flag.
It also completely stinks that such a community-friendly company like Valve has had this done to them. The have a long track-record of helping out people who want to release free extension to their games - and HL2 is to be accompanied by a Software Development Kit and tools.
At least some of the community has responded well though - one person who confirmed that the code is indeed theirs said:
I feel for Valve about now. This sucks.
I'm deleting the source just out of respect.
Fortunately, it appears that the code is about a month old and as such will contain a bunch of bugs (many people have assumed this given the pushing back of the release date) that will be obvious to Valve employees if they see them present in other games.
Interestingly, someone has joking posted:
What? No bittorrent links?
How sad. oh wait.. you're shuning sharers today? Nevermind then