I chose "custom" to so I could specify a URL under the "URL blocking" tab. I move the sensitivity slider over to "Custom" then click the "customize" button to open the dialogue, then click "URL Blocking" on the tab strip, check the "enable URL blocking" checkbox, then type my URL after clicking "add". Afterwards, click "ok" on dialogue, and "ok" on the control panel.
When I re-open the control panel, the sensitivity is set back to "Normal".
This is an XP machine and I run CyberSitter and the CyberSitter key logger too. Othewise, standard stuff.