The US Federal Bureau of Investigations (FBI) has seized a server from a New York data center as part of an investigation into bomb threats against University of Pittsburgh, one of the server’s users, an organization called Riseup.net, said earlier this week.

The server was operated by an internet service provider called European Counter Network (ECN). One of ECN’s services is Mixmaster, a remailer service that erases digital traces of sent emails to prevent anyone from identifying their origins.

The colocation facility involved was shared by Riseup and May First/People Link.

The former provides alternative means of digital communication to “people and groups working on liberatory social change.” The latter is a self-described politically-progressive member-run ISP, whose organizational structure is similar to that of a co-op.

In a statement, Riseup said academics, artists, historians, feminist groups, gay-rights groups, community centers, free-speech groups and others were disrupted by the seizure.

“The company running the facility has confirmed that the server was removed in conjunction with a search warrant issued at the request of the FBI,” Jamie McClelland, director of May First/People Link, said.

“The server seizure is not only an attack against us, but an attack against all users of the Internet who depend on anonymous communication,” he said.

Devin Theriot-Orr, a Riseup spokesperson, said FBI was using a “sledgehammer approach” when it shut down service to hundreds of users because of the actions of one anonymous person.

“This is particularly misguided because there is unlikely to be any information on the server regarding the source of the threatening emails,” the spokesperson said.

According to Riseup, “anonymizing services”, such as Mixmaster, are used to protect identities of human-rights activists whose whistle-blowing puts them and their families in “grave danger”.

“Remailers are also important for corporate whistle blowers, democracy activists working under repressive regimes, and others to communicate vital information that would otherwise go unreported,” Riseup said.