Alternatively called a security hole, a vulnerability is a security weakness in a computer system that permits unauthorized or unwelcome access. For example, an Internet browser could have a vulnerability that crashes the browser or grants someone else access to files on your computer when you visit their site.
To help detect vulnerabilities vulnerability scanner tools locate weaknesses in networks or programs. These tools are computer programs that gather information which is used by an attacker to gain illegal or unauthorized access to a network. The information may determine what computers are present and the operating systems they are running. Once that information is known, then known exploits or recent vulnerability discoveries may be carried out on the targeted system.
Several computer security companies also offer vulnerability scanners and programs that help detect vulnerabilities on networks and keep it more secure. Costs for security software can vary greatly from a free assessment to high-end report that costs over $30,000.
When a vulnerability is detected in software, its developer must update or patch the insecure code. However, if the program is no longer supported by the developer, it cannot get fixed and remains vulnerable. If the vulnerability is with a network, it would be up to the network administrator to correct it.