The researchers were able to obtain the information by using software to automatically scrape profiles.
According to Wired, the head researcher, Aarhus University graduate student Emil O. W. Kirkegaard, added in an online journal's forum (which has since been suspended for legal reasons), "Some may object to the ethics of gathering and releasing this data. However, all the data found in the dataset are or were already publicly available, so releasing this dataset merely presents it in a more useful form."
Vox points out that it's a breach of ethics according to the American Psychological Association, which states that people involved in research studies have the right to consent.
Even worse, Wired suggests that it's possible — though unconfirmed — that the researchers created an OkCupid profile so they could access the data and run the scraping bot.
The big problem if those allegations are true? The researchers may have collected and released information that users only make available to other logged-in users, not the general public.
Kirkegaard has not responded to questions from several publications, but told Motherboard that he "would like to wait until the heat has declined a bit before doing any interviews. Not to fan the flames on the social justice warriors.”