Trade secrets can be found in player-developed (non open source) add-on software and in economically valuable, non-publicly-observable methods used by players to enhance their gameplay.

FORBES: Online Games And Crowdsourced Creativity: The Next Frontier In Intellectual Property

Aimster is an add-on to the software that lets users swap files with the people in their buddy lists.

BBC: Ready, Aimster, Swap