In May 2011 a European Union law was passed stating that websites that leave non-essential cookies on visitors' devices have to alert the visitor and get acceptance from them.
This law applies to both individuals and businesses based in the EU regardless of the nationality of their website's visitors or the location of their web host.
What are 'non-essential cookies'?
Non-essential cookies are basically those which aren't required for the website to function. For example, if cookies are needed for a customer to check out and buy products, that is considered an essential cookie.
Examples of non-essential cookies include (but aren't limited to) those from analytics, advertising and affiliate networks such as Google Analytics, Google Adsense, and all affiliate programs. The vast majority of websites drop non-essential cookies, and it's more than likely that your website contains a mix of essential and non-essential varieties.