Whenever users try to leave a comment, register, or login, they are recorded in the Good Cache if they pass or the Bad Cache if they fail. If a user is blocked from access, they are added to the Bad Cache. You can see the caches here. The caches clear themselves over time, but if you are getting lots of spam it is a good idea to clear these out manually by pressing the “Clear Cache” button.
Bad IP Cache Size
You can change the number of entries to keep in your history and cache. The size of these items is an issue and will cause problems with some WordPress installations. It is best to keep these small.
Good IP Cache Size
The good cache should be set to just a few entries. The first time a spammer hits your site, s/he may not be well-known and once s/he gets in the Good Cache, s/he can hit your site without being checked again. Increasing the size of the cache means a spammer has more opportunities to hit your site without a new check.