Port Scanner :

A port scanner is a piece of software designed to search a network host for open ports. This is often used by administrators to check the security of their networks and by crackers to compromise it. To portscan a host is to scan for listening ports on a single target host.

1. Nmap
2. Superscan
3. Angry Ip Scanner

1. Nmap

Nmap (”Network Mapper”) is a free and open source utility for network exploration or security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap runs on all major computer operating systems, and both console and graphical versions are available.

www.nmap.org

2. Superscan :

SuperScan is a powerful freeware TCP port scanner, that includes a variety of additional networking tools like ping, traceroute, HTTP HEAD, WHOIS and more. It uses multi-threaded and asynchronous techniques resulting in extremely fast and versatile scanning. You can perform ping scans and port scans using any IP range or specify a text file to extract addresses from. Other features include TCP SYN scanning, UDP scanning, HTML reports, built-in port description database, Windows host enumeration, banner grabbing and more.

www.foundstone.com/us/resources/proddesc/superscan.htm

3. Angry Ip Scanner :

Angry IP Scanner (or simply ipscan) is an open-source and cross-platform network scanner designed to be fast and simple to use. It scans IP addresses and ports as well as has many other features.

It is widely used by network administrators and just curious users around the world, including large and small enterprises, banks, and government agencies.

It runs on Linux, Windows, and Mac OS X, possibly supporting other platforms as well.

www.angryziber.com/w/Home

Linux Security is a big topic and is difficult to be covered in one post. i will keep posting on this top time to time.

Below is some basic information; how we can secure a linux box.

1. Password Security
2. Directories Permissions/Ownership Security
3. Unnecessary Services
   
4. Network Security

1. Password Security

Make you password strong and lengthy. Combine letters, numbers, and symbols. Use password meter to test your passwords. Do not use root login for your normal work. only use limited users and for installation and other tasks where root login is required you can use su or sudo to become root and perform special task as soon as you are finished with your task press ctrl+D to return to normal user envirement.

2. Directories Permissions/Ownership Security

Linux have very good directory permision system as compared to Windows. All you need is to only change directory permissions where needed. and do not permit access to directoires like /etc /root to limited users as they could read important information that would help them hacking you box. You can use online permission calculator to calculate permisions .

3. Unnecessary Services
You need to disable all services that are not usefull to you. you can use sysv-rc-conf to check and manage all servces and their run levels. To disable a service you can uncheck a service run levels in sysv-rc-conf .

4. Network Security

Network Security is its self a big topic but at basic level you need to check which network services you are running at your linux server ( for example apache/httpd mysql bind ) . You can use firewall to disallow unneccessary access to these services . IPTABLE or IPCHAIN is firewall that is widely used to secure linux server. but for unauthorized access you need to configure each service to disallow. i will try to go in deep details of these services so stay tunned .

Your Comments will be appreciated.