hmmm.. I think law enforcement agencies need to stay in accordance with the law even with their "discovery". Breaking into someone's IE or exploiting vulnerabilities in order to get information otherwise you wouldn't be able to get falls under breaking into someones "property", I think, even if its "just" an Internet browser.

Therefore, you "legitimate" search warrant will be thrown out of window by a judge, and classified as the Fruit of the poisonous tree.

http://en.wikipedia.org/wiki/Fruit_of_the_poisonous_tree