These Levels don't have a Secret:
99Dog1.lvl
98Dog2.lvl
99Dog3.lvl
22Hacker.lvl
34Free.lvl
There's a really good steam community guide by Cpt. Falconator found here:
https://steamcommunity.com/sharedfiles/filedetails/?id=63277...I personally used Maka91s Video Guide from Trueachievements found here: