Want to tweak the Albert Einstein or Christina Aguilera entries on Wikipedia? Too bad, they are in the "protected" category.

This NYT article explains:

At its core, Wikipedia is not just a reference work but also an online community that has built itself a bureaucracy of sorts — one that, in response to well-publicized problems with some entries, has recently grown more elaborate. It has a clear power structure that gives volunteer administrators the authority to exercise editorial control, delete unsuitable articles and protect those that are vulnerable to vandalism.

Those measures can put some entries outside of the "anyone can edit" realm. The list changes rapidly, but as of yesterday, the entries for Einstein and Ms. Aguilera were among 82 that administrators had "protected" from all editing, mostly because of repeated vandalism or disputes over what should be said. Another 179 entries — including those for George W. Bush, Islam and Adolf Hitler — were "semi-protected," open to editing only by people who had been registered at the site for at least four days. (See a List of Protected Entries)

While these measures may appear to undermine the site's democratic principles, Jimmy Wales, Wikipedia's founder, notes that protection is usually temporary and affects a tiny fraction of the 1.2 million entries on the English-language site.

"Protection is a tool for quality control, but it hardly defines Wikipedia," Mr. Wales said. "What does define Wikipedia is the volunteer community and the open participation."

From the start, Mr. Wales gave the site a clear mission: to offer free knowledge to everybody on the planet. At the same time, he put in place a set of rules and policies that he continues to promote, like the need to present information with a neutral point of view.

The system seems to be working. Wikipedia is now the Web's third-most-popular news and information source, beating the sites of CNN and Yahoo News, according to Nielsen NetRatings.

The bulk of the writing and editing on Wikipedia is done by a geographically diffuse group of 1,000 or so regulars, many of whom are administrators on the site.

"A lot of people think of Wikipedia as being 10 million people, each adding one sentence," Mr. Wales said. "But really the vast majority of work is done by this small core community."