I have used this tool on a couple of occasions, last time using the most recent version, and same things happen each time, it hangs on determining list of updates needed, after installing .net, silverlight etc. I have found that installing KB3083324 and KB3087039 appears to cure the issue, and updates are found after about 10mins.
Also last time I used the tool, my system rebooted a couple of times, and hung. I manually rebooted OK, but the admin account created did not delete itself.
Just thought this may be useful. KB3083324 is the most recent update agent.