When Eric Le Bourg, a French biogerontologist, came across a paper in a Korean journal recently, he almost fell off his chair; the entire article — text and graphs included — had been taken from one of his earlier articles. "It was plagiarism from beginning to end," he says. "I was astonished; it was pure cut and paste."

Such blatant copying of an entire article is not unknown, says Harold Garner, a researcher at the University of Texas Southwestern Medical Center in Dallas. Garner's team has used its eTBLAST text-matching software to build Deja Vu, a continually updated database that already holds some 75,000 abstracts listed in Medline that seem highly similar. His team has so far found dozens of near-100% clone papers.

I was astonished; it was pure cut and paste.

Garner estimates that among the 181 papers they have identified so far as duplicates, 85% of the text is similar on average, but one-quarter share close to 100%. For a full list of the most similar pairs of articles, click here There are currently 22 'repeat offenders' in the database. These are authors who have published at least two articles that do not share authors (and so are putative or known plagiarisms). On average these people have 'authored' four papers, ranging from two to ten, and spanning 12 countries.

Le Bourg's paper, "A review of the effects of microgravity and hypergravity on aging and longevity" was published in the Elsevier journal, Experimental Gerontology (E. Le Bourg Exp. Gerontol. 34, 319–336; 1999). The duplicate, by Hak-Ryul Kim, who listed his affiliation as the biology department of Korea University in Seoul, was published a year later in the Korean Journal of Biological Sciences (H.-R. Kim Kor. J. Biol. Sci. 4, 231–237; 2008).

Le Bourg and the editors of Experimental Gerontology have tried to investigate further, but to no avail. They contacted authorities at Korea University but got no response, Le Bourg says. E-mails to Kim were not returned. He seems to have left the university, says Bourg, who hasn't been able to track down Kim's current affiliation. Meanwhile, the Korean Journal of Biological Sciences has ceased publication.

With the trail gone cold, Experimental Gerontology intends to publish a note in its next issue stating that its editors have done their best to elucidate the case, and that "in the absence of any explanation, we believe that this is plagiarism of our article that we want to bring to the attention of the scientific community".

Garner has begun to systematically contact editors and authors of the duplicates he has identified to assess how other cases have been followed up, and is submitting the results for publication. Many journal editors seem reluctant to pursue cases of plagiarism, and half of the articles that editors are alerted to remain uncorrected, Garner says. Few journals have communicated their retraction decision to PubMed, the most widely used abstracts database.

But the wider availability of tools to detect duplicated text is empowering editors. John Loadsman, an editor of Anaesthesia and Intensive Care, who is a researcher at the Royal Prince Alfred Hospital near Sydney, Australia, is one of several editors who been using eTBLAST. He is 'policing' the anaesthesia literature and says that he has already found three cases of duplication. Other publishers are using an anti-plagiarism tool called CrossCheck, which employs text-matching algorithms by iParadigms, a software company based in Oakland, California.

Many of the duplicates in Deja Vu come from non-English-speaking countries, and some scientists have asserted that a degree of plagiarism is justified as a way of improving the English of their texts (see _Nature_ 449, 658; 2007). "There definitely is a cultural component," says Garner, "but this appears to be an equal-opportunity behaviour, with scientists from across the world involved."

When confronted with their plagiarism, some researchers can be brazen. One offender, whose paper shared 99% of its text with an earlier report, wrote to Garner: "I seize the opportunity to congratulate [the authors of the original paper] for their previous and fundamental paper — in fact that article inspired our work."