Users are urged to take precautions and make sure they patch the flaws now.
According to the Microsoft Security Bulletin, two of the flaws are what are called buffer overruns, and would allow an attacker to download material onto an infected computer. The third flaw relates to what is known as the remote procedure call, and could be used to allow the attacker complete access to the computer.
Taken together the flaws, carrying Microsoft's maximum alert, allow the hacker to launch a denial of service attack – where a server is so overloaded with requests that it crashes. It's all very similar to the chaos caused by the recent MSBlaster worm.
The MSBlaster worm spread rapidly around the globe and infected over 500,000 computers by the time it tried to launch its denial of service attack on a Microsoft site. It had the unfortunate side effect of causing infected computers to crash and reboot every few minutes.
The new flaws affect the following:
Security company Symantec has warned that it believes "that active exploitation and creation of internet worms targeting this vulnerability is imminent." Users are urged to download the relevant Microsoft patch immediately.