The shared user ID allows applications to share data
and application components. In order to be assigned a
shared user ID the two applications must be signed with
the same digital certificate. In effect, the developers can
bypass the isolation model restrictions by signing
applications with the same private key. However, since
there is not a central certification authority, the developers
are responsible to keep their private keys secure. By
sharing the user ID, applications gain the ability to run in
the same process.