Sqlnuke.B is a nuker type hacking tool.
A nuker is a program that sends information packets to remote computers. If too much data is received in a short period of time, the affected computer can block, restart, etc. If the affected computer is a server, then it results in a denial of service.
Additionally, a nuker can damage the Windows Registry, the file system or key files needed for the correct functioning of the computer.
Sqlnuke.B does not spread automatically using its own means. It needs an attacking user's intervention in order to reach the affected computer. The means of transmission used include, among others, floppy disks, CD-ROMs, email messages with attached files, Internet downloads, FTP, IRC channels, peer-to-peer (P2P) file sharing networks, etc.