Tier 1 - Typos/Very Small Bugs - $50,000
Tier 1 bugs are errors in spelling, or other very small, insignificant bugs. Ones that most people wouldn't even notice, and have no bearing on actual game play.
Tier 2 - Miscellaneous/Non-Major Bugs - $150,000
Tier 2 bugs are more significant bugs in the game that are clearly evident, but have no bearing on actual game play.
Tier 3 - Significant, but Non-Abuseable Bugs - $500,000
Tier 3 bugs are significant bugs that have an effect on game play, but do not have the potential to be abused or exploited.
Tier 4 - Major, Abuseable Bugs - $5,000,000 + Immunity
Tier 4 bugs are very serious bugs that can be exploited by players. Abusing any game bug is a bannable offense, so reporting a Tier 4 bug offers you immunity from being punished for abusing the bug.