New Microsoft security updates.
One odd little bug with all the updates I've gotten for Internet Explorer is that the updates always toggle a little box in the "Advanced" settings labeled "disable script debugging." A number of web sites used to throw out a box complaining about a script run time error, asking me if I wanted to debug. It took a long time to find that little toggle the first time.
Now, when the updates flip it back, at least I know right away what to do. If the updates change any other settings, I don't know what they are.