It is sometimes necessary to use a proxy to preserve anonymity while surfing the Web. Still there are software tools that allow to determine the real IP address of the visitor even if he was using proxy server. However they are less efficient in the case of using shared proxy because administrators guarantee the anonymity of their clients.
Let’s consider the basic options that allow to determine the real IP-address of a specific user:
1. "Breadcrumbs" in the form of Cookies can be stored in the browser - during one session or permanently. Although there is no direct link between cookies and proxy there still remains a possibility that user first launches an unprotected (not anonymized) browser, enters his password that will be stored in cookies, and then re-authorizes through a proxy server. The virus-spy software could detect such activities, cookies will be compared with the original IP-address and the user will be revealed.
2. Browsers’ modules / plugins / add-ons are in fact the least secure channel of the whole system. They make it possible for viruses and other malware soft determine the real IP-address of each user. The only way to protect users’ computer against such a determination is to abandon the installation and install only checked and proven additions (that are officially permitted by browser developers). At the same time almost all browsers are free and they are therefore provided on an «as is» basis - so there is nobody to claim.
3. "Black Lists" also known as RBLs (Realtime Blackhole List – an online list of "black holes"), are the bane of all proxy servers. However such lists contain only free proxies which are often used for illegal purposes. That is why free proxies soon after their appearing become objects of additional attention of "web-fighters" who secure Internet finding illegal activities. To increase the security every user should pre-test the specific proxy in the RBL services or organize his own proxy server for an extra charge. Fortunately today the cost of shared proxies is very democratic and their benefits are obvious.
Shared proxies moreover are the only possible to organize a completely anonymous server because when using the free services even a chain of 20 different proxy servers will be available for the web-provider.