When Windows XP was originally shipped in October 2001, it included a limited firewall called "Internet Connection Firewall". It was disabled by default due to concerns with backward compatibility, and the configuration screens were buried away in network configuration screens that many users never looked at. As a result, it was rarely used. In mid-2003, the Blaster worm attacked a large number of Windows machines, taking advantage of flaws in the RPC Windows service. Several months later, the Sasser worm did something similar. The ongoing prevalence of these worms through 2004 resulted in unpatched machines being infected within a matter of minutes. Because of these incidents, as well as other criticisms that Microsoft was not being active in protecting customers from threats, Microsoft decided to significantly improve both the functionality and the interface of Windows XP's built-in firewall, rebrand it as Windows Firewall, and switched it on by default since Windows XP SP2.