Thank you for contacting Websense Technical Support, this is Freddy and I have taken the ownership of this case.
Issue Reported : You want to know why are you getting alerts that you have accessed jdn.monster.com, even if you have not accessed jdn.monster.com. (Correct me if I am wrong)
Websense Logging Services get log information(user activity info) from Websense Filtering Service. Filtering Service does filtering based on Http GET requests. So even if the GET request to jdn.monster.com is triggered from an Ad on some other site, the request will still count as Job Search.
This is as per the design. If you want to increase the threshold you can do so by navigating to Web Security-->Settings-->Alerts-->Category usage.