I have noticed that on a daily basis I will get a hit or two from diferent websites I am totally unfamiliar with. I will then look at the site and see no link there to mine. Thus, how does it happen that I show a hit or two from these unfamiliar websites?
They might be hijacking your site's content or keywords. Perform a google search using your domain and those you are unfamiliar with to find some answers and if you have access to your site's logs check carefully the targeted URL as they might also be hackers trying to find a security hole or email crawlers trying to steal information from your customers or visitors if any is stored on the server.
They could be using a script to mock your site to think its got a refferal from their site when it hasn't, meaning a typical webmaster would be curiouse and actually visit that site to see where it's coming from - its a marketing method. Could be easily done using a addon for firefox.
I think in most cases it's something less ominous-referrer spam. This is a technique which causes your website to be visited by the spammer's site. It will therefore show up in your stats as a referral...and when the curious webmaster goes to find their link, it gives them a hit with a high likelihood of Alexa ranking, since most webmasters have the toolbar. This way, they have real-looking traffic. I think this is just a technique to enhance Alexa, they get everyone.
I was totally oblivious to this until now, For the past 4 years this has been happening to me, god, lucky i dont have the crappy toolbar