(The 'bat signal', as the media has dubbed it, is actually a cat. Image: http://internetdefenseleague.org/)

The Cyber Intelligence Sharing and Protection Act (Cispa) being tabled in the US aims to aid investigation of web attacks. It could also, however, allow authorities to spy, and compromise people's privacy by exposing their browsing habits.  To co-ordinate protests against the draft law, activists have set up an internet signalling system.