If there are multiple update panels on the page say Upd1 and Upd2. There is a button placed in Upd1. How can you stop Upd2 to update when button placed in upd1 is clicked?

Answer:

There is a property called UpdateMode which takes two values
1.Always : Default value of this property.
2.Conditional

When set to conditional, then that updatepanel's content only gets updated when control placed in that update panel does a postback. Control placed in other update panel will not affect this updatepanel.