A group of anonymous internet activists have surged to prominence in Germany by examining the doctoral dissertations of politicians for plagiarism on a public Internet site.

The so-called plagiarism hunters helped rock the German political establishment last month when popular Defense Minister Karl-Theodor zu Guttenberg resigned after he admitted to copying part of his doctoral dissertation.

In a way, it's kind of a hobby seeing how good the dissertations are in question of authenticity, Debora Weber-Wulff, a professor of media and computing at the HTW science university in Berlin, told Reuters on Tuesday.

But the anonymity of the internet activists has raised questions about their ethics, especially if the allegations prove to be unfounded, plagiarism expert Volker Rieble told Reuters.

On the one hand it's good that people are paying attention to this, said Rieble, a law professor at Ludwig-Maximilians University in Munich.

But it's problematic that they're alleging plagiarism anonymously. The accused don't know who's attacking them.

Since the Guttenberg plagiarism scandal broke in February, plagiarism hunters have raised questions about other dissertations on the collaborative VroniPlag Web site http://de.vroniplag.wikia.com .

We have been sweeping a lot under the table and not talking about it, Weber-Wulff, a VroniPlag collaborator, said about academic plagiarism. It's rampant.

The group said over a quarter of all pages in the thesis of German politician Silvana Koch-Mehrin, the vice president of European Parliament, contain instances of plagiarism.

Heidelberg University, where the dissertation on historical monetary unions was conferred, set up a review panel earlier this month. Koch-Mehrin, a member of the pro-business Free Democrats, has yet to address allegations against her.

There are about 15-20 users who contribute often to VroniPlag and a handful who are sporadically active, Weber-Wulff said, adding that at least 10 percent of a thesis must appear to be plagiarized before it goes public on the site.

But Weber-Wulff disagrees that the group's anonymity does irreparable damage to a person's reputation.

It's not a question of who says it, she said. They're not accusing anyone of plagiarism, they're saying, 'Can you explain why no quotes were used?'

(Editing by Paul Casciato)