The Code Red worm was a computer worm first observed on the Internet on July 13, 2001. It attacked computers running Microsoft's IIS web server. The worm spread itself using a common type of vulnerability known as a buffer overflow. It did this by using a long string of the repeated character 'N' to overflow a buffer, allowing the worm to execute arbitrary code and infect the computer. The worm propagated and infected systems faster than anyone's ability to download and install the necessary corrective patches.