Roundup provides the ability to manage access to each of a classes
properties (ie. View, Edit, etc.). For properties that users do not have
View permissions for the current value of a property will be displayed
as '[hidden]' in the node journal/history. The problem is that
older/previous values for the same property are not sanitised at all, so
users can view information that they probably should not be able to.

example:
Date                 User     Action  Args
2015-01-12 02:27:11  user1    set     secure_prop: Old Value2 -> [hidden]
2015-01-12 02:26:48  user1    set     secure_prop: Old Value -> Old Value2
2015-01-12 02:26:43  user1    set     secure_prop: Old Value

Ideally the properties that users do not have View access to should
probably not appear in the journal/history at all.