Purism has started a petition for Intel to either release an ME-less CPU design or open-source it. Intel ME(Management Engine) is sometimes also known as AMT or vPro.(Though vPro is an umbrella of multiple technologies.) Note non-vPro CPU's also have Intel ME integrated, it's part of all modern Intel CPUs. https://puri.sm/posts/petition-for-intel-to-release-an-me-less-cpu-design/ More technical details can be found in this paper: http://blog.invisiblethings.org/2015/10/27/x86_harmful.html
Here's some: http://www.slideshare.net/codeblue_jp/igor-skochinsky-enpub Afaik there's some privileges it has such as direct memory access etc, but I don't know all the details. There is also a thread on Wilders here but with the terminology being confused I don't think everything there is correct information and also not sure on what exactly applies to ME and what to other technology. https://www.wilderssecurity.com/threads/secret-3g-intel-chip-provides-backdoors.353866/