Question: I have a Macbook Air 13" (mid 2012) on which I installed Windows 10 via Bootcamp a while ago. It all runs smoothly and works fine except for the WiFi. 

The internet connection breaks frequently (which means that I am not able to access the internet). I am though still connected to the WLAN network at any time (often it says "no internet, secured"). Disconnecting and reconnecting to the WLAN network is the only way to get it back to working. I noticed the same behaviour in different networks. Other devices do not show interrupts.

When using OS X the connection is fine all the time.

I already reinstalled the broadcom driver and deactivated the option that the system can disable the device for energy management reasons (I don't know the exact name of this option in english, sorry).

What else can I do? Did anyone have the same issue or a similiar one? Thank you in advance for responding.

Answer: 
Deinstalling Cisco VPN Client fixed my problem. 

There seems to be a problem with updating from Windows 8 to Windows 10 when Cisco VPN Client is installed (<https://superuser.com/questions/947651/no-network-connection-after-upgrading-to-windows-10>). 

Although my Windows 10 was a fresh install, deinstalling Cisco VPN Client helped me getting a stable internet connection.
I had a similar problem on my iMac with Bootcamp (iMac 5k, Windows 10 build 1511, Bootcamp 6). Wlan and audio were not working after Windows Update. I resolved this by disabling Hyper-V:

1. Control Panel > Turn Windows Features On and Off
2. Uncheck the "Hyper-V" checkbox
3. Restart