MS05-019 is not categorized as virus, worm, Trojan or backdoor. It is a group of critical vulnerabilities in the TCP/IP protocol on Windows 2003/XP/2000 computers, which allows arbitrary code to be remotely executed in the vulnerable computer. DoS (Denial of Service) attacks may also be launched exploiting these vulnerabilities.
If exploited successfully, MS05-019 allows hackers to gain remote control of the affected computer with the same privileges as the logged on user. If this user had administrator rights, the hacker could take complete control of the system: create, modify or delete files, install programs, create new user accounts, etc. However, most likely, these vulnerabilities lead to denial of service attacks, degradation of network performance, reset of TCP connections, etc.
These vulnerabilities are usually exploited by creating a specially crafted TCP/IP, TCP, IP or ICMP (Internet Control Message Packet) packet and sending it to a vulnerable computer.
If you have a Windows 2003/XP/2000 computer, it is recommendable to download and apply the security patch for this vulnerability. Click here to access the web page for downloading the patch.