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 . There's even a business case to be made . 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.

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