Datalogix uses information obtained through loyal-shopper programs—email addresses and other identifying data—to match up customers with their Facebook accounts. That process allows Facebook advertisers, who have long wondered if Facebook ads lead to purchases, to have some sense of whether their advertising is actually driving spending...

...Good for Facebook and Datalogix. If, on the other hand, you'd prefer Facebook to not know when you buy toilet paper or tampons at a CVS, here's how to opt out of their weird tracking (as you can imagine, finding out on Facebook how to opt out is a Byzantine process): Just go to this page and, under "Choice," click the opt out link.