This has probably been around a long time, but I just noticed the following at the top of an Amazon web site I visited.

"Hello, X Name. We have recommendations for you.", where X Name = my Initial & Surname. 



So where do they get that info from?

I have never bought anything off Amazon, though I did try to MANY (maybe 8+) years ago. (Tried to buy a small hardware item, but of course discovered they will not ship hardware internationally)