Ok to tell you things from the start I cleanup computers for the public I have a phone/computer repair shop, I received a computer 2 weeks ago and I turned it on and is was windows 8 and I logged in. After logging in I was faced with a black screen and a cursor, thinking it was a virus I hit ctrl + alt + del and started the task manager and opened my flash drive with my anti virus scanners. Avg or Sophos was the one that finally killed it once it was removed the desktop just popped right up no issues and I finished cleaning and done. I haven't heard from the customer since so there was no issues. I got a call from a lady about a mile down the road from him saying her computer was need cleaning so I brought it in and cleaned it only a couple of high risk viruses but got those done and I put avg antivirus when done and it was out the door. A few days later that same lady called back saying there was a black screen on her computer. She brought it in and this computer is running windows 7 and it had the same what I call virus on it that the windows 8 one had ran the virus scans and done. She told me it happened after doing a flash player update. That was last week. I just received a call saying the windows 7 computer has a black screen again after trying to update windows, what I'm trying to figure out is this a virus or what, and what is causing it? A simple virus removal gets rid of it but why does it keep happening?