It appears that my computer has been hijacked by one of the groups that will get you back on line?

That happened to me twice. I immediately shut down my computer completely. Then waited a few minutes and started my computer back up. The hold was gone. It happened to my son too. So try shutting down completely and then log back on. When that happens again just immediately turn off your computer. Don't call the number they provide. That gives them another link to contact you. My son did and they harrassed him for awhile. I told him to tell them you were going to call the police and they stopped calling. This scam is called ransomware. It is well known by the virus companies. It is usually hiding in a post on fb. You click on the post and you get caught. The posts I clicked on were really interesting I thought, Like somebody famous just died. Or someone famous is very ill. Don't fall for them like I did. Hope this helps.