In both Chrome and Explorer on my PC, I am prevented from accessing some sites, being told in a pop-up window that in order to gain access I must first sign up for a "free account", prompting me for a user name and password, then asking for my credit card information. The business name is sometimes given as "gravenfun.com" and sometimes as "Jabirufun".
My Norton 360 detects no virus or malware, nor does Norton Power Eraser which I just now downloaded and ran.
A Google search resulted in my trying a different anti-virus program, "StopZilla", but it did nothing but waste my time as well.
This malware is present on two PC's, a tablet and a phone, and what I would like to avoid is the time and trouble of reinstalling their operating systems.
Any and all advice will be sincerely appreciated.