We all know that Java Virtual Machine is a virtual machine means a software that executes Java ByteCode. It is the one who provides Java and WORA (Write once, run anywhere) architecture.
Starting with J2SE 5.0, changes to the JVM specification have been developed under the Java Community Process, JCP as JSR 924.
It's a matter of month, Sun going to make Java open source. The hottest debatable issue is of JVM, becasue experts have the opinion that for each problem statement developers will change the JVM according to their convience. Let's see Sun is going to do something for it. This particular concern is relatively big since there already a number of competing Java VM's and few of which are fully compatible.
Some of the open source implementations of JVM like Kaffee and Waba are comparable to closed source implementations of Sun's Java HotSpot, Blackdown and BEA systems. Anyway the current issue for Sun is to retain the Java, Platform indepedent which may be at stake after making Open Java.
Talking about the secure execution of remote code, Java follow "sandbox" mechanism, which is desgined to protect the user from misbehaving or malicoius code. Publisher can apply for a certificate with which to digitally sign applets as "safe", giving them permission to break out the sandbox and access to sys local file.