Every Windows program has its own Zero-Days. Zero-day means the flaws present in the windows program which allow Hackers to intrude any computer. These zero-days are very rare and if some computer expert finds it he can sell it in millions of cash. There is a special Black-Market for this purpose where these zero-days are auctioned and the person offering highest price gets the windows flaw. Windows-XP had four zero-days the team made for the preparation of Stuxnet bought these zero-days at high price and used them for the given task. Moreover the team also used drivers (software) of two companies of Taiwan illegally. These drivers had their certified Signature which allowed Stuxnet to cheat antivirus program. It started its working when a specific program was installed in P-1 computers which were monitoring Centrifuge. This virus affected almost 100000 computers in the world mainly damaging the computers in Indonesia, India, Azerbaijan, Iran and Pakistan. In April 2010 the new version Variant was introduced which not only destroyed the target Centrifuge but also affected lots of computers in general.