I keep getting a popup that says I should delete "ryder" because it will "damage my MacBook". Is this for real?

I am having a persistent problem with redirects. Lately, on certain sites, the browser keeps opening windows without my asking it to. In particular, there is a redirect to a fraudulent PayPal site. There is also a warning that popups up about a couple of different files - one is ryder and the other is a name I can't remember. The warnings tell me to delete the files. I need to get all of this to stop. Please advise...