System and methods for an overlay disk and cache using portable flash memory

A computer readable medium having stored thereon instructions for performing a method of software virus prevention comprising:

• scrambling functionally equivalent code segments located on a plurality of different computers to form a machine-specific code layout for each computer in the plurality of computers;
• retrieving a scrambled code block from a first computer of the plurality of computers that is functionally equivalent to a code block of a second computer of the plurality of computers;
• converting the code block from the machine-specific code layout of the first computer to canonical form;
• and
• re-scrambling the code block for use on a virtual machine running on any one of the plurality of computers.

A system for software virus prevention comprising:

• means for scrambling functionally equivalent code segments located on a plurality of different computers to form a machine-specific code layout for each computer in the plurality of computers;
• means for retrieving a scrambled code block from a first computer of the plurality of computers that is functionally equivalent to a code block of a second computer of the plurality of computers;
• means for converting the code block from the machine-specific code layout of the first computer to canonical form;
• and
• means for re-scrambling the code block for use on a virtual machine running on any one of the plurality of computers wherein the scrambling, retrieving, converting and re-scrambling means are all in operable communication with each other.