The European Union's cookie directive—dismissed by one entrepreneur as "stupid to the core"—comes into force on Saturday and sites that fail to implement the regulations face the prospect of legal action.

The directive requires that users of a website must give "specific and informed indication" that they consent to a cookie being stored on their device. Consent must involve some form of communication where the individual knowingly indicates their acceptance; it isn't enough to include a general consent in site's terms and...