Carlos is getting a popup telling him he's been hacked. He's got OS X Lion on his Mac. Leo says that there's a new thing called "ScareWare" which makes people think they have been hacked or have a virus and it won't let them exit the browser until they call a number. But in reality, it's just a popup that's designed to scare people into calling so that they can convince them to install a remote app that will allow the to do something to "fix" it.
Leo says he's probably OK. If he really wants to be safe, he can disconnect from the internet and then reboot. He should go to his browser and see if it pops up. He should also look for things he doesn't recognize in his browser extensions and delete them. There could also be a plug in.
This is why Leo recommends people use a Chromebook. Samsung makes a good one for around $500, but there are decent ones for $200 as well.