How filters work to keep surfing clean
- By Eric Kulisch
- Jan 07, 2001
More than two dozen filtering products crowd the market these days in response
to increasing demand from schools, libraries and private users. Though the
products all work to block objectionable content, most differentiate themselves
with various options and levels of protection.
First-generation filters either stopped Internet pages from loading
with manually created databases of sites to avoid, or rigid lists of banned
words. One approach missed too many sites, while the other let too many
To keep up with Internet sites that proliferate at a rate of several
thousand each week, filter makers now say they use software with advanced
artificial intelligence to mine the Web for text streams. Those that fit
certain criteria are automatically added to a list of sites to filter.
Several industry officials say the algorithms built into their software
can analyze words in context so that, for instance, the word "breast" does
not block access to breast cancer information. And they claim teams of editors
review the flagged sites to make sure innocent material is not caught in
the electronic net.
The newer software allows content to be screened page by page to preserve
access to a site where some pages are desirable and some aren't. Customers
can decide which content categories — sex, violence, drugs, hate or even
sports — to filter.
Some services can block chat room discussions, e-mail and newsgroups,
or let subscribers customize their approved or restricted lists and adjust
filtering levels for users of different ages. WebClean, from Lernout &
Hauspie, gives customers the choice to substitute characters for offensive
Filtering software housed on a network server generally is more sophisticated
than the versions people load onto home computers. At some institutions,
Internet traffic is routed through a network hub or a central server managed
by the filter maker or an Internet service provider. Others use an on-site
or proxy server at each location.
When someone tries to access a site, a short query asks the central
computer if the site is appropriate. The server compares the address of
the requested page to a list of pre-screened addresses. If the site is
appropriate, the server retrieves the address. If a site is blocked, the
user will generally get a blank screen with an error message indicating
the site has been blocked.
Companies often download updated lists on a daily or weekly basis.
Many companies offer filtering as part of larger security and Internet
management software packages. To keep library patrons from squatting on
a computer or to help students stay on task, officials can plug in software
that turns off the computer after a set amount of time.
Monitoring and tracking software, such as Cyber Sentinel by Security
Software Systems Inc., allows network administrators to capture screen views
and log addresses users visited on the Internet.
The makers of Cyber Sentinel tout features such as real-time monitoring
of e-mail and instant messaging and the ability to recognize, block and
capture messages from predators and pedophiles. The software can be combined
with another product that displays and forces a user to accept an organization's
acceptable use policy before using a specific application.
N2b Inc.'s Bess Filtering Service, named after the inventor's dog,
and other programs include built-in caches of popular, approved sites. By
storing Internet protocol addresses, a browser doesn't have to wait for
sites to download, reducing network congestion and increasing access speeds
without expensive bandwidth upgrades.