Wikipedia and others who participated in an unprecedented Internet blackout Wednesday have brought their sites back online with the promise to keep their battle going against the contentious Protect IP Act (PIPA) and the Stop Online Piracy Act (SOPA).

In a message on its website, Wikipedia thanked the people who supported its blackout yesterday, but said, "We're not done yet."

Wikipedia was one of several large websites participating in the Internet "strike" yesterday. The site blacked out its content and replaced its usual homepage with a message warning visitors about the two anti-piracy bills. Other sites that did much the same thing included Reddit, BoingBoing, Tucows and an estimated 10,000 or more smaller websites.

Search giant Google participated in the protest, too, but did not black out its site. Instead, it blacked out its main logo.

Fight for the Future, one of the groups that organised the protest said that four of the top 10 Internet sites, 13 of the top 100 and another 40,000 smaller sites took part in the blackout. Of those numbers, 37,000 of the sites that went dark were on, the organisation said. It also offered an online rundown of statistics related to the online protest.

In all, more than 4.5 million signatures were collected and two million emails sent through groups such as the Electronic Frontier Foundation (EFF), Demand Progress and Fight for the Future, the group said.

According to the EFF, between 9 pm Tuesday and this morning, nearly 396,000 people signed its online petition, resulting in close to 1.2 million emails to Congress.

"Our next action against the blacklist legislation is a call-in day to senators on Monday," said Rainey Reitman, activism director at EFF. "We've seen incredible successes in the last 48 hours, but we need to make sure this proposal is good and dead before we let up. Ideally, I'd like to kill this bill so thoroughly that Congress won't even think to introduce a replica."

Tiffiniy Cheng, co-founder of Fight for the Future, said the group plans to carry on its protests until both bills are dropped. "Unfortunately, the Protect IP act is still scheduled for a final vote this Tuesday" in the Senate, Cheng said. "We haven't heard from Senator [Patrick] Leahy yet that he is pulling the bill."

Fight for the Future plans to ask Interent users to flood the phone lines of their local representatives starting January 23. The group's main website will also host a live audience participation stream where protesters can submit their concerns to a handful of senators who plan on filibustering the vote, she said. The group is also trying to organise a series of in-person meetings with senators around the country, Cheng added.

Brock Meeks, communications director of the advocacy group the Center for Democracy and Technology (CDT), which also participated in the blackout, said traffic to its site increased tenfold.

"As of this morning, the traffic is still running close to that increase," Meeks said. He added that CDT plans to stay engaged with the new "geek lobby" that appears to have sprung up in opposition to SOPA and PIPA. "We will continue to be active in monitoring the legislative process going forward and will make our expertise in this area available to congressional staff, if they choose to call on us."

According to Wikipedia, its main blackout page was viewed by more than 162 million visitors. More than 12,000 people left comments on the Wikimedia Foundation's blog post, while eight million people looked up contact information for their local representative's using a Wikipedia tool.

"The purpose of the blackout was twofold: to raise public awareness, and to encourage people to share their views with their elected representatives," Wikipedia's message said.

Despite the protests, the bills are far from dead, Wikipedia cautioned. "SOPA and PIPA are symptoms of a larger issue. They are misguided solutions to a misunderstood problem."

Security vendor ZScaler yesterday pointed to a noticeable increase in traffic to Wikipedia's site during the blackout, mostly from Internet users apparently curious to see what the site looked like. While the number of users rose, the number of transactions per unique user was much smaller compared to normal, ZScaler blogger Mike Geide noted, "This behaviour could be described as 'online rubber necking'".