Like any social network, LinkedIn has to deal with the issue of fake profiles. It turns out the process of building those profiles is highly automated: an unknown person or group has been using Amazon Web Services (AWS) virtual machines to scrape data from LinkedIn and make duplicate profiles.
LinkedIn has filed a lawsuit in the US to try and identify the person or people responsible for what it says is the creation of "thousands" of fake accounts using automated bots. According to the lawsuit, those accounts are then being used to try and attract candidates to online recruiting services. Given that recruiting is one of LinkedIn's sources of income, that's clearly something the company needs to take pains to avoid.
LinkedIn has systems in place to try and prevent scraping of its sites, but no system is completely impenetrable. One lesson? Check LinkedIn profiles carefully before accepting a connection — if details seems incomplete or strange, you may well be dealing with a rogue "clone profile", not the real thing.