I have downloaded a dmg file called BaiduYun_2.2.0.dmg, which, on double-click, shows the license agreement window straight away, instead of showing an installation package or an application that can be dragged to the Applications folder. I have never seen any installation on Mac OS X like this before. Is there an autorun setting anywhere that I can disable this behaviour? Additionally, it does not show up as a mounted device on Finder windows.
A DMG can be set to display a license agreement before it will allow you to open it. This is normal and nothing to be alarmed about. Once you accept the license agreement, it will mount and open the normal Finder window showing its contents.
There is no way to disable it and nothing is being auto-run.