Google introduced interest based advertisements and it asked to change the privacy policy of your website since it will use cookies to analyse the user interests and display ads according to that. user can opt out from this feature , they have given option for that also. You might have got an email with all those details.
If you want to disable this feature
1. login to Google Adsense
2. Go to account settings
3. find Interest-based Ads Preference and click edit
4. Change the settings and save
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