Are you by chance trying the Touchdown Venus version? https://play.google.com/store/apps/details?id=com.nitrodesk.venus.nitroid
If so, it could be because that seems to be a pre release version. Any pre release apps can be prone to false detections from AV products.
If not the Venus version, which version have you installed? I see there is an older and a newer version for Android V2 and for the rest.
What device and Android version are you using?
Where did you install Touchdown from?