Sometimes we'll ask someone if they have Google Analytics installed but they don't know if they do or not.

This isn't as strange as it seems, it may have been installed by the web developer when the site was built, but because no one has never checked the stats, it's been forgotten about.

This is what is known as Referral Spam.

Referral spam will show up as strange site address's, or address that don't make sense as referral sources, in your Google Analyics reports under Acquisition.