Although the price of bandwidth has been reduced recently, it is still costly enough that users should to be ensuring usage is legal and that no unauthorised users are 'tapping' into their bandwidth. There is only one foolproof way to prevent this – 'port locking'. This is achieved through use of a Remote Authentication Dial-In User Service (RADIUS) server in conjunction with the new IEEE 802.1X Port-Based Network Access Control standard.

This is according to Danie Fourie, director at XDSL, an Internet Solution Provider (ISP) catering to the needs of business and consumers.
He explains: "Theft of bandwidth is growing in the South African market. It is sometimes unintentional or even unwittingly authorised by the owner of the account. The most common occurrence is when a user 'lends' his user name and password out to friends or relatives who make use of the account. However, this 'sharing' of bandwidth is rarely recalled when the bill arrives and the user finds he has exceeded his bandwidth allocation and is paying a premium for the extra Gigabytes used. However, there are more sinister means of bandwidth theft. It is as simple as 'stealing' the person's login details."
While it is a criminal offence to steal bandwidth it is difficult to prosecute the perpetrator as an interdict is required for Telkom to provide the physical address of the port in question to the police. This has further reinforced the need for ISPs and businesses to begin using RADIUS servers in conjunction with the new IEEE 802.1X Port-Based Network Access Control standard as it allows the ISP to present the port address to its customer.
Fourie explains: "Port locking is a control measure that monitors the port numbers that initiate or request the bandwidth connection. The ISP will register the port number that is authorised to make use of the account and is able to identify unauthorised port numbers are making use of the service."
XDSL's Webadmin, an online administration tool for the end user, allows users to set up access rules if they are mobile or need to make use of another PC with a different port number, allowing them to lock into multiple ports.
In addition to mismanagement, another common cause for unauthorised bandwidth usage is viruses. They can install themselves as a Windows service and often anti-virus software will not detect the virus.
Fourie advises: "Users should have a proper anti-virus solution installed that has user rights rather than administration rights activated. This will  prevent viruses circumventing the anti-virus software and installing itself as a Windows service."