Unwanted plug-ins

At the end of my working day, sometimes more often, I delete unwanted cookies from my computer (iMac), also clear cache and history, using CCleaner;
Yesterday, after deleting, I noticed that the number of cookies and other website data exceeded the number I keep. When I checked manually, I found that the extra items were all plug-ins of some sort from sites I'd not heard of.
DAK please whether websites can install plug-ins without the user's consent and if so is a a new trend to get round the cookie law? In any event whether CCleaner can do this or another app that can delete them without my having to do so manually?
Thank you.

So it definitely is plugins which have been installed into your web browsers without your consent? This definitely sounds like you have a malware infection on your computer.