What's up with this 'Win 7 Security' on my gf's laptop?

ok so today my gf tried to get on the internet and this keeps coming up and says the internet could harm her computer, and won't let her get on the internet. i go to the firewall and see what's up with that, and it says the firewall is off(idk why she doesn't even know how to get to it, and my mom had it before her and she didn't either) and when i try and turn it back on it won't let me(can't remember exactly what it says but it brings up something saying i need to dl something and pay for it and some other **** like that) how do i get rid of this? it's getting on my nerves, listening to her not being able to get on her computer. all she does is get on facebook, WoW and Rift.