Here a tutorial how to fix the following error:
An issue with your computer is blocking the VAC system, You cannot play on secure servers
There are many points you can try posted in this article on steam link
The issue was fixed for me by the following:
1.) Exit steam (kill the process in the background)
2.) Run repair command:
- open command prompt
- execute "C:\Program Files (x86)\Steam\bin\SteamService.exe" /repair"
After that you should see a message:
Steam Client Service "C:\Program Files (x68)\Steam" repair completed.
You might need to reboot your computer.
This should do the trick.
Edited by redy., 09 July 2017 - 01:53 PM.