github nmap/npcap v0.05-r8
Npcap 0.05 r8: Improved driver signing method

Now Npcap driver will be signed in both SHA1 and SHA256 digest algorithms and with timestamp. This improvement will help the driver installation on Vista and Win7. This is an issue reported by Graham Bloice (see graham's answer in

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:
KB3033929 for Win7 with SP1:
This step should requires reboot.
More information please refer to:

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.

latest releases: v1.55, v1.50, v1.40...
5 years ago