Malwarebytes scan finds something called pup and mywebsearch. What are they and how did they get on my computer? I didn’t download them.

When Malwarebytes scans and finds a program that could potentially be harmful to your PC, it comes up as a PUP which stands for potentially unwanted/unsafe program.  You can then decide for yourself if you want to have Malwarebytes remove it for you by checking on the tick box next to the result.  Mywebsearch is a junk toolbar that gets into your computer when you download free stuff like games, music, pictures, etc… To remove mywebsearch, go to add/remove programs and look for mywebsearch in the list of programs installed on your computer.  Then uninstall it.  Also, go to manage add ons and disable it, if it shows up there.