Adobe Air is reinstalled to an older version

Hello, I have work in my school with free program Scratch 2, this program needs Adobe Air from version 8 to newer version.

When I install first time Adobe Air 28 (actual version) and Scratch all is ok, but after some days I find that Adobe Air is installed automatically with older version 3.5.

With this version Scrach doesn't work. How is it possible?

System: Windows 7 pro.

Thanks