It's a poorly programmed code of the Update subsystem, and I've located the problematic function spending all of the CPU time: https://news.ycombinator.com/ite

It's a poorly programmed code of the Update subsystem, and I've located the problematic function spending all of the CPU time: https://news.ycombinator.com/item?id=11267019 https://news.ycombinator.com/item?id=11267019 wuaueng.dll!CUpdatesToPruneList::AddSupersedenceInfoIfNeeded The bug is obviously in highly inefficient traversal through the existing info about the updates, which didn't degrade to being so obviously bad at the time when there was just a small number of the updates. I've used Microsoft tools to diagnose that, and I'm not the only one who has found it, http://www.dslreports.com/forum/r30535980-WIN7-MS-updates-taking-too-long~start=90 http://www.dslreports.com/forum/r30535980-WIN7-MS-updates-ta... so the same info is available to Microsoft, but they obviously don't want to fix it. On my machine it takes some 4 hours using 100% CPU of one core. If there are only 100 millions of such machines, and if it's just 40 Watt hours used during these 4 hours, it gives some 4 Gigawatt hours wasted every month in the world due to that particular bad code (If I calculated it right, over one year, it's a rough equivalent of the total energy use of 1500 Germans or 500 US citizens.)