Yahoo secretly monitored customer emails on behalf of US intelligence - report

US internet firm Yahoo searched its own customers' emails at the request of US intelligence officials, according to Reuters' sources.

The National Security Agency (NSA), or CIA, issued a directive to the company to scan hundreds of millions of email accounts, to which it complied.

Yahoo was instructed to search for a specific set of characters within their email database, but the reports do not specify what the intelligence officials were searching for.

According to the sources, special software was created by Yahoo on behalf of the government in order to comply with the request.

The allegation comes shortly after the news that 500m users' data had been hacked from Yahoo Mail accounts.

"Yahoo is a law-abiding company, and complies with the laws of the United States", a statement from the company said.

Yahoo is currently in the process of being taken over by telecommunications giant Verizon in a $4.8bn agreement.