It was probably a contractor. That’s what intelligence experts are saying about the source of the massive WikiLeaks dump of CIA documents this week.

Though authorities don’t appear close to naming a suspect in the so-called Vault 7 leak, intelligence community sources VICE News spoke to agree that the leak most likely originated from a private contractor employed by the spy agency.

In addition, both the Wall Street Journal and Reuters report that investigators believe the leak came from private-sector contract workers, and that CIA officials have been aware of the breach since last year. The 7,800-document release from WikiLeaks includes details about technologies the CIA uses to surreptitiously break into smartphones, smart TVs, and other digital devices.

Glenn Carle, a former CIA operations officer who worked at the agency for 23 years, said it makes sense for the leaks to have originated from contractors.

“The standards of security and professionalism among contractors are lower,” he said. “There’s this exponentially growing body of people with access to highly sensitive information, who are theoretically held to the same standards [as agency employees], but in practice don’t have them.”

Since Sept. 11, 2001, the number of private contractors employed by the U.S. government has skyrocketed, said Steven Aftergood, executive director of the Project on Government Secrecy at the Federation of American Scientists.

“Contractors were able to assume many of the necessary but mundane tasks of the intel community,” he said. “IT functions, human resources functions, everything from payroll to groundskeeping. In some cases, they also perform intel-related functions themselves.”

The contracting explosion has certainly not been without its problems in the past. In 2007, for example, the Senate Intelligence Committee found that private contractors on average cost nearly twice as much as in-agency staff. A 2012 CIA report found that the agency violated federal laws by hiring outside contractors for intelligence work that was supposed to be performed by agency employees. And Edward Snowden, who arguably became the most celebrated and vilified whistleblower in history when he leaked classified information about U.S. government surveillance to journalists in 2013, was an NSA contractor at the time of the leaks.

Tim Shorrock, author of “Spies for Hire: The Secret World of Intelligence Outsourcing,” says that the growing role of private firms in intelligence work is directly related to a rise in the number of large security breaches.

“It’s almost certain that [the recent CIA leak] came from contractors,” he said. “The risks of such leaks are much greater with contractors, and the evidence is in the last two years.” Shorrock has estimated that 70 percent of the intelligence community’s budget is spent on contracting.

Snowden worked for contractor Booz Allen Hamilton, as did Harold Martin, a 52-year-old NSA contractor living in Maryland who was indicted in February for allegedly taking sensitive national security information and storing it in his home over the course of 18 years.

Booz Allen is one of the five corporate contractors that employ about 80 percent of people contracted to work for U.S. spy agencies. Aftergood said that these contractors are “one step removed” from the Congressional and intra-agency oversight that government employees face, and are instead “subject to the supervision of their contracting agency.” Shorrock said there doesn’t appear to be adequate amounts of oversight of contractors.

“They see themselves as one big happy family,” Shorrock said of the spy agencies and contractors, pointing out that people often switch relatively freely between working directly for the government and working for contracting firms. “They don’t see a differentiation. And a lot of these contractors, they have the highest levels of security clearance.”

As an example, he brought up Mike McConnell, a U.S. Navy vice admiral who served as director of the NSA from 1992 to 1996. He then left the NSA to become an executive at Booz Allen. He left Booz Allen to become the Director of National Intelligence in 2007. He returned to Booz Allen in 2009 and is currently listed as a senior executive advisor at the firm.