In return, the journals demand fees they had not previously disclosed that can be as high as several thousand dollars, the F.T.C. said. When authors ask to withdraw their papers, they often are refused. And some academics who are described as editors on the journals’ websites in fact are not editors, and are not even aware that their names are being used.

These practices stand in sharp contrast to those of legitimate scientific journals, where editors send papers to experts for review, a process that can take weeks or months, and often ask for extensive revisions. Those that charge authors clearly publish their fees.

And no editors are listed without their knowledge. Legitimate journals also are indexed — listed in places like PubMed, run by the National Library of Medicine — giving them a stamp of approval. Predatory journals claim to be indexed but are not, the F.T.C. said.

Over the years, academics have tracked predatory publishers with a blacklist, first published by Mr. Beall and now published anonymously. In one sting operation, a fictitious researcher with fake credentials applied to be editor at a list of journals. She was accepted enthusiastically by many predatory journals, and spurned by legitimate ones.

Academics often get daily solicitations from these journals. On Wednesday, James DuBois, director of the Center for Clinical Research Ethics at Washington University in St. Louis, forwarded to The Times an email he had just received.

“It is learnt that you have published a paper titled ‘The Role of Culture and Acculturation in Researchers’ Perceptions of Rules in Science’ in SCIENCE AND ENGINEERING ETHICS and we are impressed by the subject,” the email said. “So we wish to invite you to contribute other precious papers of related topics to the journal.”