Write Your Own Attack Scripts!
One of the best features of Nessus is the ability to write your own plug-ins. Nessus allows its user to write plug-ins in the C language or a custom Nessus Attack-Scripting Language. These custom plug-ins can interface with a defined Nessus Application Programming Language, supporting interaction of various plug-ins with the knowledge base of the current active scan. The customizability offered by NASL really makes Nessus shine and allows an active community of developers to create numerous plug-ins quickly and easily.