Hi Ian, Mgid ads are caused by adware - you should uninstall all suspicious applications using Control Panel. After this procedure you should also scan your computer with legitimate anti-malware (Spyhuter, Malwarebytes Anti-malware) - https://www.pcrisk.com/top-spyware-removers Both of the mentioned programs are great at detecting and eliminating adware. In your case this should remove the unwanted ads from appearing in forums and other websites.