Agnes Grudniewicz and colleagues highlight the need to define what constitutes a predatory journal (Nature 576, 210–212; 2019). History shows, however, that such journals and their publishers rapidly adapt to filters that might discredit them.

In their early days, such journals were ephemeral, with false claims of indexing, vague titles (such as International Journal of Applied Sciences and Engineering), fraudulent publication fees and dubious-looking websites. By contrast, modern predatory journals use more specific titles and release well-designed issues. They have real indexing and well-developed websites. They are owned by supposedly legitimate organizations, publish for free (because they have other interests), run counterfeit archives and safeguard themselves with plagiarism checks (see F. H. Kakamad et al. Int. J. Surg. Open 17, 5–7; 2019).

However, the skipping or faking of scientific review remain cornerstones for predatory journals and publishers. In our opinion, it is dangerous to exclude the criterion of inadequate peer review from any definition of predatory journals, as Grudniewicz and colleagues propose, because that definition would then fail to catch its criminal targets.