Hi!I just signed to say same happened to me and to my father too (who is terrible with computers) so I had to go to his home and help him. I find it very intrusive. It never asked me either. I have use windows 7 64bits.
I will keep Opera because I took the time to change defaults one by one and it seems it works fine but I was going to delete it as soon as I saw that and my father did delete it because he was worried this could happen again and he had to call me again.
Not trying to have an attitude or anything, just telling I think it's not cool.