An article was recently posted by the guys at Guru3D, explaining the latest problem with online activation of Ubisoft titles:

We already know that you can only activate the game on 3 different systems, but now it turns out that this affects hardware changes as well.

What the Guru guys did was perform a performance test of Anno 2070. After testing it on a particular rig with a particular setup, they wanted to change the graphics cards to compare the performance. That's when things started to go wrong ...

"For the NVIDIA setup I take out the GTX 580, and insert a GTX 590. When I now startup the game 'BAM', again an activation is required. Once again I fill out the key and now Ubisoft is thanking me with the message that I ran out of activations.
Here's what Ubisofts DRM is doing these days, they don't just verify the number of PCs you work on, nope ... they monitor hardware changes. So once we inserted that GeForce GTX 590 the hardware id # changed rendering our activation invalid."

Ubisoft do of course have a 'solution' to this: "simply" e-mail their support and ask them to reset the activations. I feel, however, that this falls under the category of making things more difficult for the customer than they need to be - yet another piece of evidence that Ubisoft's draconian methods are becoming too much for even themselves to handle.

P.S: I should specify that Heroes VI does not use the DRM used by Anno 2070.