A lot of sites track you. They target the ads to what they think might grab your interest and wallet.

I was reading of one store site in US that did this and sent out a brochure or some such thing of baby items. The man of the house was amazed to be sent such a thing and rang to complain it was inappropriate, then found out his teen daughter was expecting.

The shop computer had tracked purchases and made the assumption that someone there was probably expecting a baby. The computer knew before the family.

So much for privacy!