I've encountered 2 websites this week that captured my Safari window and would not allow me to close it. One was for MacKeeper and another was some other scam site telling me I needed to "upgrade my browser". I did not want to click on their pop up windows at all and was unable to get the window from reappearing without resetting Safari. How does this happen and why doesn't Safari block this? I have "Block Popup Windows" checked in preferences.