1. Get FirewallAppBlocker, or anything like it, or do it manually through win firewall
2. Search for all .exe files with win search, select them all, drag on Fab, or manually add them all to windows firewall and block
3. Launch unity, close, repeat until it fails to load (mine fails on second launch - first loads ok, then fails)

It fails either to a white screen with a loadbar, or (a new one) to just a black window.

Editor log:

LICENSE SYSTEM [2017731 13:13:24] No start/stop license dates set

LICENSE SYSTEM [2017731 13:13:24] Next license update check is after 2017-07-31T18:59:12

Built from '2017.1/release' branch; Version is '2017.1.0f3 (472613c02cf7) revision 4662803'; Using compiler version '160040219'
OS: 'Windows 7 (6.1.7600) 64bit' Language: 'en' Physical Memory: 16325 MB
BatchMode: 0, IsHumanControllingUs: 1, StartBugReporterOnCrash: 1, Is64bit: 1, IsPro: 0

COMMAND LINE ARGUMENTS:
D:\u2017.1\Editor\Unity.exe
[CEF] undefined in file:///C%3A%2FUsers%2Falex%2FAppData%2FRoaming%2FUnity%2FPackages%2Fnode_modules%2Funity-editor-home%2Fdist/assets/unity-editor-home.js at line 39
Error loading https://api.unity.com/v1/oauth2/authorize?client_id=launcher&display=launcher&locale=en_US&response_type=code&redirect_uri=launcher://unity/C%3A%2FUsers%2Falex%2FAppData%2FRoaming%2FUnity%2FPackages%2Fnode_modules%2Funity-editor-home%2Fdist/index.html#/login

(Filename: C:\buildslave\unity\build\Editor/Platform/Interface/NativeWebViewWindow.cpp Line: 51)

There is more info in this forum post:

https://forum.unity3d.com/threads/blocking-unity-from-internet.485934/