This flaw allows an attacker to gain full access to the victim's files and to the network. Understanding this flaw requires a more detailed explanation of Java packages. The Java language supports the concept of packages-groups of Java classes meant to be used together. Packages have names like java.lang and EDU.princeton.cs.sip. Every Java class belongs to some package.
Packages serve two purposes.
First, since the full name of a class is the package name followed by the classname, they provide a way for different people to name their classes without having accidental name collisions. For example, if we put all of our classes into the authors package and you put all of your classes into the readers package, then our classnames cannot collide with yours. The second purpose of packages is to restrict access to certain Java variables. When declaring a variable, a programmer states which classes are allowed to access the variable. If the variable is declared private, it is accessible only by the class that created it.