Windows Firewall has the annoying habit of letting stuff work until one day it just starts doing its job and doesn't. Typically this is through user prompts that either get spacebar'd away due to focus stealing* or blocked because the user doesn't know what it's asking about.

It's a mess working out what it's doing, fixing it and explaining to the user why their perfectly working system just broke. It could really use some organization tools like the Task Scheduler.

*I thought Microsoft promised at one point around the lead up to Windows 7 that they were going to address their stealing focus issues.