Android Handset runs a Linux operating system as background and upon which android application runs. Each application runs in separate process in Dalvik virtual machine for each application an instance of Dalvik virtual machine is created. Dalvik Virtual Machine is like the Java Virtual Machine. The Design of Dalvik Virtual Machine is optimized to be able to execute on Mobile Device. Dalvik Acquire Less Memory so that multiple instance of dalvik can be created and run simultaneously in the mobile device.
When Any application is installed in the mobile device the Linux operating system create a new user profile for that perticular application and an instance of Dalvik Virtual Machine. Each Application runs on its own Dalvik Virtual machine as separate process and its own files it doesn't share anything. so there is less chance of "Bricking" ( Bricking is called the mobile crash).
How Android Manage Security for users personal information ?
To access the shared resources on the mobile device. Android Application requires to get explicit permission to access those resources. such as camera , to make call , Bluetooth , access personal information , current location etc.
if any application A want to share its data with application B. B access A's data by using URI. for e.g. Application A manage Contact information birth data etc and if A want to share these information to other then it create the URI for accessing these data. rather than giving control of full application.