When you take surveys, get coupons, enter sweepstakes, etc., in the real world or online, you've likely authorized them to sell your info in the fine print.

They called, from "GE Home Security Systems". I said I was on Do Not Call list, and the guy laughed, said he'd call back later, then hung up on me. Ever since Home Depot took our number for a "survey" I've been getting calls from RainSoft (aka Home Depot Water Systems) - I suppose Home Depot SOLD our number to others.
I have reported this number to DONOTCALL.GOV -- Nice 10-thousand-dollar fine for them.