Is the SharePoint 2013 App Store safe or not? How to protect data from the apps?
There are two types of app store in SharePoint 2013. The first is a 'public store,' which is the main app store that Microsoft has been marketing heavily. Users connect to it from within SharePoint, and it adheres to the now standard rules of a typical store.
The other type of store is the 'corporate store' (referred to as an app catalog by Microsoft). This is a local, locked down store, which can be centrally managed by the particular organization running SharePoint. Only apps that have been specially selected and signed off can be included. In this way Microsoft has neatly sidestepped any opposition organizations might have to opening up their Intranets to cloud based app stores. If you are not comfortable with such a public store then the solution is simple, switch to a private store containing only the apps you have selected.
It is safe as MSFT have a process to approval process when you submit a app to public store and if you are using app catalog then your administrator have the permission to do so.