Now Npcap driver will be signed in both
SHA256 digest algorithms and with
timestamp. This improvement will help the driver installation on
Win7. This is an issue reported by Graham Bloice (see graham's answer in https://ask.wireshark.org/questions/46689/failed-to-create-npcap-service).
For Vista x64 and Win7 x64 users:
If you still get the pop-up window that said
Windows requires a digitally signed driver (or get error
577 when executing
net start npf), please try these steps:
1) Install Windows SHA-256 certificate security updates successfully.
KB2763674 for Vista with SP2: https://support.microsoft.com/en-us/kb/2763674
KB3033929 for Win7 with SP1: https://technet.microsoft.com/en-us/library/security/3033929.aspx
This step should requires reboot.
More information please refer to: http://www.davidegrayson.com/signing/
2) Install latest Npcap 0.05-r8.
3) If step 2) still fails running the driver, then reinstall an alternate version of Npcap you NEVER installed on the machine before (like 0.05-r7, if you unfortunately tried 0.05-r7 before step1), then try 0.05-r6.) to "flush" the driver cache. You should use the same option of
Install Npcap in WinPcap API-compatible Mode as you did in step 2). This installation of 0.05-r7 should work.
4) Reinstall back the latest Npcap 0.05-r8. This second-time installation should succeed.
If the above steps don't work for you, you can still run Npcap by disabling Driver Signature Enforcement:
Let me know if these steps work.