The slides leaked by NSA whistleblower Edward Snowden named nine companies that allegedly share data with US intelligence agencies, but according to a new report, the actual number of firms that collaborate with US spies may be much larger. Try thousands of them.

Citing anonymous sources, Bloomberg reports that information sharing between private tech companies and US intelligence agencies is virtually routine, even though very few people within the participating companies are likely to know that it's going on.

Among the information frequently disclosed is early access to software vulnerabilities, where companies give US spies access to data on zero-day security flaws before it's made available to the public.

Sometimes that information is used to shore up domestic security, the report states, but other times it's used to allow intelligence agencies to exploit flaws in software sold to foreign governments.

Microsoft spokesman Frank Shaw confirmed to Bloomberg that Redmond does participate in "several" information-sharing programs, but said that they were designed to give the government an "early start" on risk assessment and mediation.

And yet, government officials said Microsoft "doesn't ask and can't be told" how the information it shares is actually used.

Similarly, a spokesman for Intel security subsidiary McAfee said the US government is a key customer of the data it compiles on computer security threats.

"McAfee's function is to provide security technology, education, and threat intelligence to governments," the company said in a statement. "This threat intelligence includes trending data on emerging new threats, cyber-attack patterns and vector activity, as well as analysis on the integrity of software, system vulnerabilities, and hacker group activity."

In many cases, the report claims, companies voluntarily hand over information that intelligence agencies might otherwise need a court order to obtain.

Such information sharing is typically done in total secrecy, where only the highest-level executives of a company are even aware of the relationship.

Often, a sole executive will be appointed the "committing officer" in charge of disclosing information to US spies. That exec will typically be given documents granting him or her immunity from all civil prosecutions related to the information sharing.

Similarly, the report claims that the major US internet providers – including AT&T, CenturyLink, Level 3, Sprint Nextel, and Verizon – have received letters from the US attorney general indemnifying them from lawsuits under US wiretap laws.

But immunity from prosecution isn't the only thing the government has to offer. Sources claim that intelligence agencies will frequently offer companies an inside peek at their data in exchange for more of it.

For example, Google cofounder Sergey Brin was reportedly given a temporary classified clearance in 2010 and was allowed to sit in on a briefing about the hacking capabilities of China's People's Liberation Army.

Still other execs reportedly cooperate with intelligence agencies out of patriotism or a sense that they are helping to defend national security.

The types of information shared can range from customer metadata to detailed descriptions of telecommunications networks and systems, both foreign and domestic – and often the strict legality of such information sharing is unclear.

"That's what makes this issue of oversight so challenging," Jacob Olcott of Good Harbor Security Risk Management told Bloomberg. "You have a situation where the technology and technical policy is far outpacing the background and expertise of most elected members of Congress or their staffs." ®