How do advertisers know my home town?

I am starting to see adverts that refer to my home town. How do these adverts get this information? Does the browser give out my post/zip code?

For instance when I looked at the following article on CNET:
http://news.com.com/Court+rules+for+Microsoft+in+antitrust+case/2100-1014_3-6062479.html?tag=nl

I saw the following advert:

# Court Maidenhead
Find Phone Numbers Addresses & Maps for Companies & Services on 118.com
118.com

"Court" is the first word on the page and Maidenhead is my home town. Clicking it submits "Court Maidenhead" to 118.com.

Is this only applicable to the UK? or does it apply in the US as well?

Should I be worried about this? I can see that it could be used to inform me about local offers, but I am not sure that I want that. Apart from my privacy are their security considerations too?

Nev

 

They "see" your IP address. My IP address originates from my city. Nothing to worry about.

 

Thanks Whiskeyman and PeteC,

Perhaps I am getting paranoid. For a while the adverts referred to "near London" or "near Lutton" (sic) then they started to mention just Maidenhead. I wondered if there was a database being created that collected details of net users.

Maybe Demon my ISP are now based in Maidenhead. I get allocated a new IP once a day so maybe the town will be different tomorrow. Anyway I will relax now and see what happens next!

Thanks for the responses.

Nev