It was a separate firewall called Sunbelt Personal Firewall
http://www.sunbeltsoftware.com/home-home-office/sunbelt-personal-firewall/
I didn't have the Windows firewall activated when I upgraded but I have had no problems with that previously.
Sunbelt is a very tricky firewall: Once I clicked the "go to shop" button in AChat and because it tried to open my browser the firewall thought it was an ad and blocked it. Then every time i tried to go to the shop, even manually typing the address or navigating through the site, it thought it was an ad and blocked it. I had to disable the firewall to shop too
I'm sure there was some way to stop it treating the updates as unwanted changes to a program and the shop as an ad but it was pissing me off in other ways too, so it's best for me to get a new firewall. I hope that answers your question.