The Cyber Intelligence Sharing and Protection Act (Cispa) aims to aid investigation of web attacks.

But the activists say the law would erode privacy by exposing people’s browsing habits and would be used to justify domestic surveillance.

The “bat signal” system tells followers to start displaying protest materials such as website banners and petitions.

Plans for the signalling system emerged in early 2012 following protests and website blackouts in opposition to two other draft laws in the US, the Stop Online Piracy Act and the Preventing Real Online Threats to Economic Creativity and Theft of Intellectual Property Act.

The web action was widely seen as influential in the campaign that saw both those laws shelved.

In a bid to harness the wave of activism those protests started, social news sites such as Reddit and Fark joined up with rights groups and many others to launch the Internet Defense League (IDL).
Rallying point

Instead of reacting on an incident-by-incident basis, the IDL monitors threats to online privacy and let supporters know when to ramp up protests.

The IDL also said it would create protest materials such as website banners, petitions and information about how to contact politicians, so people can voice their opposition in a co-ordinated manner.

In addition, some members have embedded code on the sites they control, so protest materials are shown automatically when the “bat signal” is activated.

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