That's called browser malware, it's not something that can be downloaded to your cb so it basically does no harm other than forcing you to do a manual shut down and maybe loosing what you were doing online at that moment.

It freezes your cb with hopes that you will be suckered into calling the number it gives you and once you call the number they will ask you to pay them in order to have them unfreeze your cb.

The odds are that there will be a few people who fall for it and give them credit card/paypal/vemno info so that they can rip them off.

You did the right thing by manually shutting down right away.