If you're thinking of setting up web filtering for your organisation, OpenDNS can offer some clues. It's just published a report about the most-blocked and most-whitelisted sites of 2010.
The winner is Facebook, which takes the award for the most-blacklisted Website. No fewer than 23 percent of OpenDNS business subscribers consider it forbidden Internet territory for their workers.
Happily for Facebook, it's also the second most whitelisted Website, which is to say, it's a site that's permitted when most other sites are blocked.
Clearly, one man's waste of time is another's essential.
OpenDNS is a subscription service that can be swapped in by organizations or individuals to replace their ISP's domain name system (DNS) servers. DNS is what's used to convert human-readable addresses, such as pcworld.com, into the numerical IP addresses required by computers.
Most DNS servers simply duplicate master servers, but OpenDNS offers powerful filtering tools too. This raises the hackles of some but the fact is that OpenDNS is popular, serving 30 billion DNS look-ups every day and handling the DNS requirements of one percent of the entire Internet.
In terms of blacklisting by businesses, Facebook was followed in OpenDNS's list by MySpace, blocked by 13 percent of subscribers, and YouTube, blocked by just under 12 percent.
The latter is undoubtedly on the list due to concerns about Internet bandwidth being wasted on movie downloads. Think what happens when a funny video e-mail gets forwarded around the office. Lots of people suddenly request a significant amount of data, which can bring a Net connection to its knees.
Facebook and MySpace are probably blocked by organisations that wish to stop employees wasting work time updating their status.
Interestingly, the top 10 blacklisted addresses also include ad.doubleclick.net (5.7 percent) and ad.yeldmanager.com (1.8 percent). Both addresses typically serve adverts and their blocking might indicate privacy concerns within organisations about tracking by advertiser cookies. Alternatively, it might be that sympathetic network admins "switch off" adverts for their users.
Whitelisting allows OpenDNS users to let through sites that might otherwise be banned because the user has chosen to block entire categories of websites.
Of the popular blocking categories, there are no surprises: Pornography tops the list, followed by sexuality and then tasteless sites. The fourth most-blocked category includes proxy and anonymizer sites. Smart individuals use these to get around filtering software (hence the desire to block them!), although they're often torturously slow to use due to massive demand.
In terms of whitelisted sites, the top three are YouTube, with 12.7 percent of users choosing to let it through, followed by Facebook (12.6 percent), and Gmail (9.2 percent).
So why allow through Facebook, when so many choose to block it? Other than the "kindly admin" theory, it may well be that businesses are starting to realize the business potential of social networking. There's even a business case to be made for embracing YouTube. Blocking sites often used for fun by employees can be a knee-jerk reaction, and concerns about employee time wasting is better combated in other ways, such as employee training.
Indeed, blocking sites in any way is questionable, from an ethical point of view as well as business, although a significant proportion of OpenDNS's paying customers schools and other public bodies, which perhaps have a better reason than most. One out of three K-12 public schools in the US are customers, for example.
You can read the full OpenDNS report here.