I don't why they do this, they do it to me all the time. Last time they turned off IE on me too. Usually its my mail, and the real player. If you do a system restore, you're gonna updated again, and therefore...
Open your Start Menu. Click on "Set Program Access and Defaults". Choose "custom" and enable what you need to enable. I don't know if this is the best solution...because it changes to whatever is best for Microsoft, no matter how you set it. It will enable IE for you. I check "enable access" on all the choices except "Instant Messenger"...I don't want it, Microsoft butting in when it wants to is enough.
It seems to me if they have a program to alter settings for a download, they could have a program to reset what they altered upon its completion. I suppose Microsoft doesn't want to give the impression of being courteous.
No matter what I select, everything gets set to "use my current" within a few days to a week anyway. If you enable IE and set it as a default, it will then be considered your current browser.
In the "Control Panel" I also have "Network Set-up Wizard", as well as "Network Connections" headings, I've never been that adventuresome to employ those areas, but that might a solution also.
"Setting Program Access and Defaults" (Under "Custom") is so quick and simple and fairly goof-proof, so that's what I have stuck with. Hope it works for you too. Good Luck.
Worse comes to worse, if all that fails,
try System Restore and see if you can restore to a time before
you did the update.
start/programs/accessories/system tools/system restore