Public reactions to the disappearance of social-activist artist Ai Weiwei are escalating, much to the Chinese government's chagrin. An online petition initiated by the Solomon R. Guggenheim Foundation was brought down by Chinese hackers for a few hours yesterday. The petition—now the most popular ever to be posted on—has 90,000 signatories in 175 countries, including prominent museum officials like Glenn Lowry, director of New York's Museum of Modern Art; Nicholas Serota, director of London's Tate Gallery; and Michael Govan, director of the Los Angeles County Museum of Art. contacted the FBI and U.S. State Department's Bureau of East Asian Pacific Affairs requesting urgent assistance within hours of the attack. According to the site's founder, Ben Rattray, "All we know is that after the unprecedented success of a campaign by leading global art museums using our platform to call on the Chinese government to release Ai Weiwei, we became the victims of highly sophisticated denial of service attacks from locations in China."

Yesterday's cyber-attack also coincided with the publication of Salman Rushdie's op-ed in the New York Times describing a history of outspoken artists and writers and the risks they face—Ovid, Federico García Lorca, Susan Sontag—not least The Satanic Verses author himself. Drawing a comparison to the Soviet Union, he says "today the government of China has become the world's greatest threat to freedom of speech."

Also yesterday, the Guardian in London reported that Ai's lawyer, Liu Xiaoyuan, has resurfaced in Beijing following a five-day disappearance. Previously, Liu had posted a message on a microblog saying that he was being followed by government officials. Liu tweeted the paper to say he was fine but did not want to give any more details.

The Guardian also cited a report from the Chinese Human Rights Defenders network, indicating that another lawyer, Jiang Tianyong, had been released following a two-month detention. He too was said to be unavailable to speak to the press; the Guardian was unable to confirm his release independently. A number of other human rights lawyers and activists have gone missing since the government crackdown began in February.

Over the two weeks since Ai was taken into custody at the Beijing airport, the Chinese government has leveled charges ranging from "economic crimes" to bigamy and plagiarism. Authorities also issued a statement professing dismay at the international community's support of a "criminal." Ai's wife and several employees were called in for questioning and released, but other associates remain missing, including a friend, Ai's driver and his accountant.

On Sunday, Apr. 17, peaceful demonstrations of varying sizes were held in front of Chinese consulates and embassies in cities around the world in support of the artist. The effort was organized by the New York-based nonprofit Creative Time and announced via Facebook. Participants were asked to bring chairs for a one-hour sit-in, a reference to Ai's installation Fairytale: 1001 Qing Dynasty Wooden Chairs, which appeared in the 2007 Documenta in Kassel, Germany.

Support from outside the art world has come from, among others, the Bianca Jagger Human Rights Foundation, which is circulating a petition urging the Chinese government to release Ai. The U.S. State Department issued a statement condemning Ai's arrest as "inconsistent with the fundamental freedoms and human rights of all Chinese citizens, including China's commitments under the Universal Declaration of Human Rights."

On May 2, Ai's first major public art project, Circle of Animals/Zodiac Heads, will begin its U.S. tour in New York. The piece, a circular installation of 12 monumental bronze heads from the Chinese zodiac, each weighing about 800 pounds, was inspired by the fountain clock at Yuanmingyuan, an 18th-century royal retreat near Beijing. It is a subtle commentary on the pillaging of the original work by Western military forces in 1860; five of the heads, which are smaller than Ai's version, are missing.

In New York, the work will be on view through July 15 around the Pulitzer Fountain at Grand Army Plaza in Central Park, near the Plaza Hotel. It then goes to the L.A. County Museum of Art (Sept. 15, 2011–Mar. 15, 2012); Hermann Park, Houston (spring 2012); the Warhol Museum & Carnegie Museum of Art, Pittsburgh (Oct. 1–Dec. 31, 2012); and the Hirshhorn Museum & Sculpture Garden, Washington, D.C. (fall 2012).

Ai's installation in Tate Modern's Turbine Hall, Sunflower Seeds, comprising millions of hand-painted ceramic seeds, remains on view through May 2.

Above: Protest of Ai's disappearance in Hong Kong. Ai Wewei's sculptures will alsobe presented at Somerset House in London, May 12 - June 26.