• Don't give information to players about other players that can be used in duping scams.
• Avoid "monkey patching" - fixing code in a piecemeal fashion. Instead fix all scripts at once.
• Remember that when you add new features, the interaction testing burden increases in a nonlinear fashion.
• Fix the problem on the front-end "or it will bite you on the back end."
• Don't allow flexible inventory limits in your game. "Players will take a reasonable excess and use it pathologically," said Keating.
• Make sure your network infrastructure can support arbitrary packet sizes, but also ensure that packet sizes above a certain threshold raise warning signals.

Via Wired