CCleaner is best and most reputable Registry Cleaner. Period. Powerful scan engine, regular updates, lots of additional features and excellent price of FREE makes it the best. You may have already heard about it a lot, but if you can't find it installed on your PC download and install it right now!
Sometimes malware process or service blocks all your attempts to remove virus, trojan, worm by blocking access to Task Manager, Registry Editor, Services and does not allow you to uninstall itself from Control Panel, to remove files and folders, to stop malicious processes.
Zombie Invasion by Time Lapse Solutions is obtrusive adware for Internet Explorer, Google Chrome and Mozilla Firefox. This program does not usually install extensions in browsers, however, always double check. Main issues with Zombie Invasion are annoying ads, pop-ups, highlighted words, inline-text ads and banners like "Ads by Zombie Invasion".