Yahoo is in the process of being taken over by Verizon Communications in a $4.8bn (£3.8bn) deal. The telecoms provider declined to comment on the report.
Reuters reports that the scans were requested by either the National Security Agency (NSA) or the FBI, according to three sources - two of whom it says were ex-Yahoo employees.
The news agency says that the software scanned for a string of characters within all incoming emails, but adds that it was unable to determine what information was handed over or if other internet companies had received a similar demand.
US law allows the country's intelligence agencies to order the release of customer data that they believe could prevent a terrorist attack, among other reasons.
Companies can challenge such orders behind closed doors in the Foreign Intelligence Surveillance Court.
But Reuters reports that Yahoo decided not to fight the matter because it thought it would lose. It adds that some Yahoo employees were upset by that decision.
The whistleblower Edward Snowden, who previously revealed details about the US's cyber-spying efforts, has tweeted in response to the unverified allegations: "Use @yahoo? They secretly scanned everything you ever wrote... close your account today."
I am unsure as to what Yahoo is doing. As many of these groups get bigger they tend to quietly introduce things that they can use later on to make more money with (advertising etc) An indication of this is the organizations attempts to gain more personal details of their customers like phone numbers etc.
The customers are rarely consulted and seem to be largely ignored, despite being the reason for the organizations existence.
I would anticipate that Yahoo are setting something up that will increase their income but at the detriment to their customers. We will see what occurs in the future.
Yeah. Not worth the update. Visually similar but still tricky getting used to it. I don't know why they had to change it. It will also notify you that you've changed time zones and it hides the spam in the spam folder. You have to click it to see if you have anything in the spam folder.