The HL2 team rewrote major portions of the Source Engine in response to the hack.
Seems more likely that it was a convenient excuse.
Gosh, Valve must hire great PR. I had completely forgotten their overt evil actions around this incident.
If the hackers would have the source, they would not even need to reverse engineer the engine to build their aimbots/wallhacks.
[1] http://www.bluesnews.com/cgi-bin/finger.pl?id=1&time=1999122...