The tech giant said it was only abiding the laws of the United States.

If you have a Yahoo mail account, your private conversations might have been seen by the intelligence agencies such as the NSA or the FBI. Reuters reported that the tech giant has been scanning hundreed of millions of accounts for over a year, looking for “a set of characters” provided by spies. The article is based on statements from two former employees and another person familiar with the matter. Microsoft and Google quickly said they don’t allow their customers to be monitored by intelligence agencies.

First, Yahoo claimed they were only complying with the American legislation. Then, they called the Reuters report “misleading.”

"We narrowly interpret every government request for user data to minimize disclosure. The mail scanning described in the article does not exist on our systems," the tech giant said in a statement.

The American Civil Liberties Union said that the case is "unprecedented and unconstitutional."

“[I]f the report is accurate, it represents a new—and dangerous—expansion of the government’s mass surveillance techniques,” Electronic Frontier Foundation said in an online statement.

“The sweeping warrantless surveillance of millions of Yahoo users’ communications described in the Reuters story flies in the face of the Fourth Amendment’s prohibition against unreasonable searches. Surveillance like this is an example of “general warrants” that the Fourth Amendment was directly intended to prevent.”

According to Reuters, Yahoo complied with a classified US government directive. “Some surveillance experts said this represents the first case to surface of a U.S. Internet company agreeing to a spy agency's demand by searching all arriving messages, as opposed to examining stored messages or scanning a small number of accounts in real time,” the Reuters article reads.

The “set of characters” might had been phrases in an email or an attachment, according to unnamed sources.

At this point it’s not clear what data and how much data did Yahoo provide to the NSA and FBI.

If you care about your data and your personal information, trust no one, and encrypt everything that's sensitive. You can delete your Yahoo account and opt for PGP/GPG email encryption with any other public mail service, or even better - use Protonmail instead. It's best if the service is not US-based.

Although there's little one can do against a resourcefull entity such as the NSA, it's vital to follow the basic rules of the privacy-conscious user: encrypt everything, use strong passwords, browse with Tor and, of course, use a VPN to encrypt your internet traffic and mask your IP. Email is broken by design, therefore it's advised not to use it for communicating information that you want to remain private.