YouTube and Facebook are having a serious effect on corporate bandwidth, says Network Box.

The managed network provider surveyed 19 billion URLs visited by 30,000 end users between July and November of 2009, and video-sharing site YouTube came out top, consuming an astounding 7.8 percent of all available bandwidth.

Behind this came Facebook with 4.4 percent, Yimg (Yahoo's image search) at 2.8 percent, and Google on 2.7 percent.

Uncomfortably perhaps, Microsoft updates alone managed to eat 3.8 percent of bandwidth.

These figures are totals for the company traffic analysed, not averages, and the actual bandwidth being consumed by different websites will vary from company to company.

It is still eye-opening that only a handful of non-business websites managed to consume 21.5 percent of all bandwidth at these companies, which hints at an even greater and hidden volume being consumed by http's long tail.

The company also measured traffic volumes, as opposed to bandwidth used, and came up with a very similar list, though YouTube dropped off the top-five list entirely.

That suggests that a relatively small number of visits to Google's video website is consuming a much larger volume of actual traffic capacity, which might be expected for such a bandwidth-intensive application.

"Businesses have to be aware that their employees use Facebook at work. They should have systems in place to ensure that they are getting the best use they can from company resources," said Network Box's Simon Heron.

"This is more than a technological problem. It's about employee management."

The fact that Windows updates - patching security problems- now eats so much valuable bandwidth demonstrates that the nature of the average network is now very different to the LAN of a decade ago.

Heron was at pains to point out that a lot of http traffic is legitimate, and companies might be benefitting from some of the apparently non-legitimate traffic.

Does social networking generate business? Nobody knows, but in some cases the answer might be yes.

Equally, YouTube also hosts a a large volume of business-oriented content, as well as videos of ice-skating cats and celebrity happenings.

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See also: Twitter and Facebook costs businesses £1.38m