A patch is an update released to fix (patch) bugs, make the game more realistic and make a few minor tweaks to the game. Some patches add new elements to the game, such as more animations for the 3D Match Engine. The latest official patch is December 2009 (the other two were released in September 2009 and October 2009). After installing a patch, a new game must be created for all changes to take effect; however, previously saved games can still be played after installing a patch. To remove a patch, one must completely uninstall the game, reinstall it then download the desired patches.
The October 2009 patch contained a few updates. Among many players, it is recommended, as it is the most recent patch that contains no bugs.
The December 2009 patch only contained minor updates and was found to contain new bugs. Therefore, the October 2009 is recommended among most players.
An April 2010 patch is a massive patch update which includes a data update. It has been released officially on the forums by BGS. There is no list of changes, though it seems to have fixed some important bugs regarding wages, including other updates to the game.