An operating system is a program or set of programs that serve as an intermediate layer between computer hardware and software applications. Various operating systems are in use today to satisfy the ever changing customer demands; nevertheless the most
widespread operating systems are: Microsoft Windows, Linux/Unix and Macintosh.
Windows are mostly used as personal computers, Linux/Unix are mainly open source
while Apple Macs are often used for graphic designs or other specialist applications.
Irrespective of their application or use all operating systems up to date have been subject to security compromises or likewise failures. It is a fact that the majority of hacking tools,
viruses, worms or Trojan horses are written for Windows, but this is merely due to the
fact that Windows occupy almost 90% of the global market .Microsoft is about to release
in October 2009 a new operating system called Windows 7 .It is estimated that only in the period 2009-2010 will be shipped 177 million units, while 7 million people employed in ICT around the world will be using it (Gantz at al, 2009). For this reason Microsoft Windows OS will be our main focus.