Pop up error message

[Mervyn & Giuliana Bond]

Over the last 5 days or so, regardless of which browser I use, I have 
been getting a pop up menu saying I have a computer error and can 
have a free scan to correct the error.  In trying to close the window 
it takes over my browser window and says to click OK to start the 
free download.  There is a cancel option but after cancelling the 
offer reappears.  I force quit out of the browser to clear the deck. 
Has anyone else experienced this irritation?  What action to stop it?
Merv
--
"Science teaches that we must see in order to believe, but we must 
also believe in order to see."