Running Win8 and running IE under different user credentials can cause IE to lock up. I think it is attempting to display the initial pop-up message but failing as it is running under different credentials. Right click on the IE icon and do 'run as a different user'.
This is particularly bad if you are attempting to run under guest credentials where settings are not saved (each time the user is logged out all settings are wiped) so even one-time logging in as the user and OK'ing the dialog will not help. This is something I do when attempting to view untrusted web sites (e.g. things in spam mailbox that I'm not 100% sure are spam so I want to check). I use the guest account as it has very heavily restricted access to anything on my PC and if these websites are malicious then they can't access any of my files.
Do other people get this problem?