Drawback of URL-based Filtering.

Many program block content classed as objectionable and market them as the solution to the web content filtering problem. However, most of these programs simply filter URLs, relying on a large database of pre-classified web addresses.

The major drawback with such software is that it can only effectively filter content that has already been screened by the maintainers of the database – if a site is not in the database, this is not necessarily because it is not undesirable; rather, the software is simply unable to make any useful classification.

Given that the Internet consists of tens of billions of pages with millions more added every day, such a system can realistically only cover a tiny percentage of existing sites, and will always be fighting a losing battle against creators of undesirable content. Some particularly naïve URL filters can also be very easily bypassed.