The number of people visiting Wikipedia spiked yesterday despite the organisation shutting down in its site in protest against the US Stop Online Piracy Act (SOPA), monitoring by Zscaler Threatlab has shown.

On a normal day Wikipedia is one of the Internet’s most visited sites and shutting it on 18 January inevitably affected overall traffic volumes, the company confirmed.

However, less expected, was that the number of unique visitors to the site rose during peak hours by as much as 20 percent which it attributes to a form of “online rubbernecking.”

“This suggests that more people are flocking to Wikipedia today, but just to see the protest page and some details on SOPA,” said Zscaler security researcher Mike Geide.

“While not the goal of Wikipedia's protest, from a media and public relations standpoint these types of Internet events can stand to be beneficial or even lucrative.”

Visitors were greeted with an artfully-darkened landing page and the message “Imagine a World Without Free Knowledge,” despite the fact that pages within the site could still be reached from smartphoens and through Google caching.

The improved visitor numbers suggest that Wikipedia’s decision to risk annoying visitors for one day in return for publicising its stance has probably met its goals.

While few sites shut down altogether, several of Wikipedia’s big-brand peers altered their landing page during the protest, including Google, Wired and Mozilla.

For large sites to launch a protest like this against a single piece of US legislation is unprecedented; even more noteworthy in the long run could be that an Internet protest movement appears to have influenced the final form and course of a piece of US legislation.