Like dozens of other on-line advertising companies, Google does its best to “target” the ads you see using information it’s gathered about your browsing and searching habits. Google has now changed it's privacy policies so that it can legally serve up advertisements based on browsing history, recent searches and the message threads in your Gmail inbox.
The ad industry calls this "interest-based advertising" on the basis that they're pushing products in which you have expressed an interest. And before you sneer "yeah, right," this is the way the Internet is monetised.
This is (allegedly) anonymised data based on a profile of you rather than your identity. That doesn't stop it being creepy, intrusive and frequently annoying.
Don't like it? Well, remember if you're not paying for the product you are the product. If you don't want any ads, go elsewhere for your mail, search and other products.
How does it work? Through a tiny tracking tag, called a “cookie,” that is stashed in your browser. You’ve probably got dozens of cookies left over from most of the sites you've visited, a trail like digital crumbs, making it easy for ad networks to retrace your steps. Google takes ad “personalisation” a step further by filtering a string of your most recent Google searches.
Joshua, over on the Google Product Forums, explains it better than I can:
"Ads in gmail are always based on the content of the email you are reading. That can't be turned off. The "personalized ads" thing only affects the ability of google to use the content of other mail and searches that you've previously read to influence the ad choice. There is some more information here (although I agree it isn't very clear):"
Which is true:
If you don't want to see personalized ads on Google search, you can opt out. If you do this while you're signed in to your Google Account, you'll be opting out of personalized ads on both Search and Gmail, as well as ads on Google search that are customized for your browser.
When you're signed out of your Google Account, you can also opt out of Google search ads that are customized for your browser; however, you'll still see ads that are personalized to your Google Account.
If you don't want to see any more "personalised" ads you can opt-out by visiting Google's Ad Preferences Manager.
Next time, we'll explain a little more specifically how to opt-out of Google Personalised Ads. RC