Since "profile viewers" are a popular search term, it proves that people are trying to look at your data. Ensure your own privacy is locked down:
When you see a website offering a "Facebook private profile viewer download full version," you are usually looking at one of three things:
Enable this so that even if a scammer gets your password, they cannot enter your account.
Pages designed to generate ad revenue by promising a service they cannot provide.
You can see if you share mutual friends and ask for an introduction.