Microsoft is joining the movement to encrypt traffic that flows across its networks, citing "serious concerns" about government surveillance.
The move follows similar actions by Google and Yahoo in the wake of revelations of vast online surveillance programs led by the US National Security Agency.
"Like many others, we are especially alarmed by recent allegations in the press of a broader and concerted effort by some governments to circumvent online security measures - and in our view, legal processes and protections - in order to surreptitiously collect private customer data," Microsoft general counsel Brad Smith said in a blog post late on Wednesday.
"If true, these efforts threaten to seriously undermine confidence in the security and privacy of online communications.
"Indeed, government snooping potentially now constitutes an 'advanced persistent threat' alongside sophisticated malware and cyber attacks."
Smith said Microsoft had decided to "take immediate and co-ordinated action" to expand encryption across its services.
It is also stepping up efforts to reinforce legal protections of customer data and is "enhancing the transparency of our software code, making it easier for customers to reassure themselves that our products do not contain back doors".
"For many years, we've used encryption in our products and services to protect our customers from online criminals and hackers," Smith wrote.
"While we have no direct evidence that customer data has been breached by unauthorised government access, we don't want to take any chances and are addressing this issue head on.
"Therefore, we will pursue a comprehensive engineering effort to strengthen the encryption of customer data across our networks and services."
Major tech companies have been seeking to disclose more details about government surveillance in an effort to reassure customers, but have complained that the US government will not allow certain details to be released.
