my users been doing this to get it to work.

they would stand by the mob grinders they build and let it get lots of mobs then they would disconnect and reconnect quickly , after they do this all the mobs from the spawner that they have in their grinder give money, and exp how can I fix this ?

What's the method of killing the mobs? Are they just killing the mobs as players manually or do they have a contraption that kills the mobs?

they make them fall and take fall damage, then they relog quickly and kill them to gain xp and coins. i made it so anything the spawner spawns doesnt give nothing I also enabled the config that watches how far from spawner.

Mobs from spawners are tracked as well as the distance check if enabled. However, mobs that spawn from large "dark rooms" and other natural spawn method exploits will not be tracked at all.

idk if you understand the mobs that are giving them money are from the spawner.

still got this problem people on my server are rich...

Hmm, the mobs from the spawners should be marked with metadata to check for farming. Let me test drive your config to recreate the issue on my test server. You can post it on pastebin.com or pastie.org and put the link in this issue.

http://pastebin.com/EFfeJ1UM

here you go thanks.

I realized this is an old issue but I have tested the config and mobs that originate from spawners are marked and do not drop anything or give coins.

I did observe that the marked mobs do not survive a server restart.