rollback segment

[AK]

I have recently found that one temporary rollback segment in system tablespace is having more then 600 extnets . It looks like previous dba created this rollback segment at the time of db creation and forgot to take it offline . Now how do I find it this rollback segment is being used actively . I see values in gets , writes from v$rollstat view .   What step should I take to drop this rollback segment . What implication might have if I take this offline ? I want to relase the space taken by this rollback segment ( >600 extents ..thats big ) , so just taking offline wont do this.   Are there any views accessible from system( no sys) account which can tell me which trasaction is using which rollback segment .     thanks -ak