Data entry scams or home based typist job con typically target people searching for 'work at home' business chances. Data entry scams can have numerous variations, but a lot of them involve deceptive people into buying affiliate marketing materials in the name of data entry work.
Most people would picture data entry work to involve entering data in a database or something alike. But that is not the case at all. If you join such a website or program, you will be asked to endorse products online or offline using advertisement that you will have to type (or write). They are probable to provide you with some advertisement templates/samples that you can copy and use it yourself. So just because you will be typing those ads, they are referring to it as data entry typist job.
Once you have the ads prepared, you can circulate those ads using various means. Most usually you will be asked to use PPC or pay-per-click advertisement, such as Google Adwords and others. They might also give you ready made website that you may use to earn some money. By websites, they mean the webpages only. Domain registration and website hosting charges will be your own. You will have to spend your own money to put up those ads and hopefully someone will click on those ads, buy the product you are promoting and only then you will receive some payment.
The products that you would be asked to advertise are typically from ClickBank, which is one of the several free-to-join affiliate networks. One call also finds real data entry or writing jobs in self-employed websites.
Essentially, what is being referred to as data entry work is really Affiliate marketing or Internet marketing. Associate marketing itself is not a scam. Lots of people are working and earning from home using associate marketing. But it is a scam to hoodwink someone into buying something that is not what is made out to be.