instanceIn a blow to Windows Phone, a technical change made by Facebook’s Instagram service is preventing users from uploading photos via the popular — but unofficial — third-party Instance app for Microsoft-powered smartphones.

The change in Instagram’s system was designed to boost security. It affects a variety of apps, not just Instance, but it’s a particularly tough pill to swallow for many Windows Phone users who had turned to Instance in the absence of an official Instagram app.

An Instagram spokesperson confirmed to GeekWire via email that Instagram “recently made an update to the systems that it uses to fight spam to help prevent future attacks and increase security. As part of this, applications accessing Instagram against the terms of the API may also be affected.”

In my own usage this morning, a picture uploaded from Instance to Instagram on my Windows Phone didn’t actually appear on Instagram, at least not that I was able to see.

A picture shared to Instagram from the new Hipstamatic Oggl app for Windows Phone — which is using the Instagram API with official approval — did show up in Instagram. However, the Hipstamatic app offers only partial Instagram integration, and doesn’t allow users to view photos from Instagram. Instance was a full-featured Instagram app.

Instance developer Daniel Gary says on Twitter that he’s doing everything he can to fix the problem, and hopes to work out an arrangement with Instagram. He also concedes that this is one of the risks of being an unofficial app.

Microsoft, which was an investor in Facebook prior to its IPO, has been under pressure to get an official Instagram app on Windows Phone but has so far been unable to make it happen. At an internal company town hall meeting last week, Microsoft CEO Steve Ballmer reportedly acknowledged the need to land an official Instagram app.

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