Microsoft has quietly changed the terms of its TechNet subscription service by reducing the number of product keys made available for download to its users, The Register has learned.

On 15 September Redmond lowered the number of product keys dished out to TechNet subscribers from 10 to a maximum of five, in Microsoft’s latest effort to stamp out software piracy.

However, MS made the switcheroo without first informing its subscribers of the tweak to its TechNet small print. Product keys are used by Microsoft and other software vendors to certify that a user's copy of a particular program is genuine, and they typically require online activation.

When the change occurred, even some of Microsoft’s own employees were apparently caught out by the product key reduction, with some telling customers that there was a bug in the system.

Some subscribers who later contacted Microsoft’s TechNet team were told that the company lowered the number of product keys made available for download as “additional security measures”.

The change hasn’t hit long-term subscribers to the service, because Microsoft left those keys in place.

“We did not take away any keys. Just the amount of keys available ‘ad hoc’ via the portal has been reduced, all previously claimed keys are still available,” it said.

“The reduction is due to an updated anti-piracy policy. More information will be made available for all customers soon.”

Microsoft's new policy means that TechNet Professional subscribers now get access to a maximum of five product keys, while TechNet Standard subscribers gain access to just two keys.

But as Reg reader Jon Aubrey – who tipped us off about the change – told us, new TechNet subscribers have been “stung hard” by the reduction.

“The first thing I knew about it was when I went to download a new key for MS Office 2010 and found there were no more keys to get out of my 10 keys, when I only had registered two of them,” Jon said.

“I contacted Microsoft twice and both times had the ‘there is a bug in TechNet, don't worry’ - until I was told to directly contact the TechNet team, who told me that they'd reduced the keys under our noses without informing us.”

El Reg has asked Microsoft to tell us more about the TechNet product key rejig, but it hadn’t got back to us with comment at time of writing. ®