If you want hostile actors working directly within the Image with a full environment, then Pharo is probably not suitable.�� Its easy to get hold of global class from the Playground references and overwrite/compile any method in the system like this...

SomeClass compile: 'initialize

�� �� MyEvilHack dostuff.

�� �� ^ super initialize '��

You might want to consider Newspeak, which runs on the same VM as Pharo and has a focus on security.