The Federal Trade Commission announced Wednesday that it has stopped six “massive” tech support scams that may have duped consumers out of millions of dollars.

According to an FTC release, telemarketers tricked people into buying a “service” to remove non-existent viruses and other malware. Users were also convinced to grant telemarketers remote access to their machines. The FTC called the scams “outrageous and disturbing.”

The agency has frozen the assets of companies involved in six of these scams. It has also taken measures to block phone lines and Web sites the companies used to contact consumers.

The FTC said it worked with its counterpart agencies in Canada and Australia to identify and track the scams. Microsoft also played a part in identifying the scammers. Call centers were located around the world, but were largely concentrated in India, the agency said.

“These so-called tech support scams are the latest variation of scareware,” FTC chairman Jon Leibowitz said in a press conference. “Today’s announcement is a wake-up call to computer users around the globe.”

So far, the agency has identified at least 2,400 complaints in the U.S. related to these firms, though FTC officials said they have heard over 40,000 complaints about this kind of scams.

David Vladeck, who leads the FTC’s consumer protection bureau, said he suspects that the number of victims may be ”substantially higher.”

The operations worked like this: Telemarketers pretending to be affiliated with anti-virus firms or Microsoft cold-called consumers about supposed computer problems — often in violation of the do-not-call registry list.

They directed consumers to a Microsoft Windows menu, and told them that standard warning messages displayed there indicated malicious programs were already on their machines.

Consumers were then convinced to grant the telemarketers remote access to the computers. Scammers “removed” the non-existent malicious programs and downloaded additional software.

In addition to calling consumers, groups also bought ads from Google to advertise their false services, Leibowitz said.

The companies named in the filings are: Pecon Software Ltd., Finmaestros LLC,  Zeal IT Solutions Pvt. Ltd., Virtual PC Solutions, Lakshmi Infosoul Services Pvt. Ltd., and PCCare247, Inc. The agency also targeted individual and corporate defendants in each of the cases.

None of the companies could be immediately reached for comment.

Leibowitz also used the press conference to call on the Senate to pass a bill that would extend the FTC’s ability to coordinate its investigations with foreign countries.

The House has already passed a bill, the Undertaking Spam, Spyware and Fraud Enforcement With Enforcers Beyond Borders (U.S. SAFE WEB) Act that would extend those measures through 2020.