Microsoft made the offer in a blog post on July 1.

Announcing it was opening its first Transparency Centre at its head office in Redmond, the company's vice-president of trustworthy computing, Matt Thomlinson, wrote: "Our Transparency Centers provide participating governments with the ability to review source code for our key products, (to) assure themselves of their software integrity, and confirm there are no 'back doors'."

The revelations of blanket NSA spying by former contractor Edward Snowden have shown that big technology companies like Microsoft, Google, Facebook, Yahoo! and Apple have all willingly handed over whatever data was sought. In addition, Snowden revealed that the NSA was picking up data from these firms on the sly.

Along among these companies, Microsoft has made the most noise about fighting back. Some months ago, it said it would host the data of foreign clients outside the US, but a judgement in the US put paid to that move, ruling that no matter where the data was stored, it would be subject to US government jurisdiction.

Microsoft is also fighting a government warrant to turn over emails from its subsidiary in Ireland; the government claims these communications are relevant to a drug-trafficking operation. This fight began before Snowden's revelations.

There appears to be a fear among technology companies that if Microsoft is forced to do the government's bidding, then American cloud businesses which operate in other countries could stand to lose a lot of business.

Snowden's revelations have led to a drop in overseas business for at least two technology firms - Cisco and IBM. Additionally, the Boeing company lost an order from Brazil, which opted to go with Sweden's Saab for $US4.5 billion worth of aircraft.