Yes Facebook does quite a lot to protects their users from viruses. I have never encountered a virus when I was on their website. I have also never heard of anyone I know encountering a virus when they were on the website. So all in all I do think that Facebook is doing enough to protect users from viruses.
Facebook does not do enough to protect its users from viruses or spammers. There are always hackers on comments or posts saying to "like this page to view". Once you like it either you're page is going to be hacked or your computer starts acting funky. They should definitely figure out more ways to protect users.
I don't believe that they do. A few of my friends have had very invasive Facebook viruses in the last few weeks. They have had to cancel their accounts because it was getting so bad and spamming all their friends. If Facebook had a decent site these viruses wouldn't be happening
Facebook doesn't offer its users enough protection on anything! They rarely do anything about reports, they don't do anything about harassment and bullying. It's super easy to pick up a virus too! So many people I know have been hacked because of something they saw on Facebook, or even because there was a video or post on Facebook.