Network Secruity Scanner

Any one can test their Netwoks and to remove weakness from their networks,
Their are many softwares for this purposes,but very few people have idea of that softwares,but this post will help anybody to know how to scan their networks to remove weakness and to choose software to scan Networks,
Below are some very good softwares for this purpose,so use it share it to others and if u like this post then dont forget to comment on it, here are the links,:.
http://www.nessus.org/nessus/
http://nmap.org/
Not only this u will fine many many many useful things in these websites Especially in number 2   so readers enjoy it and share it to others.....