Update, Tuesday 10:23 am: On Monday evening, Grindr said it would stop sharing information about users’ HIV status with third-party companies. The change will happen with the app’s next update.

Add Grindr to the list of companies with creepy data-sharing practices: The gay dating network is revealing information about its users’ HIV status with third-party companies.

According to a BuzzFeed News report by Azeen Ghorayshi and Sri Ray, Grindr furnished two companies, Apptimize and Localytics, with data on users’ HIV status and the last date they were tested for the virus.

Grindr hired the companies to optimize their dating app, part of what Grindr chief technology officer Scott Chen told BuzzFeed were “standard practices in the mobile app ecosystem.”

But it’s not clear why analytics and online engagement partners would need information about people’s HIV status. Grindr, which calls itself “the world’s largest social networking app for gay, bi, trans, and queer people,” has not yet responded to Vox’s request for comment on that question.

Health experts say this could add to the stigma around HIV. “Sharing users’ HIV status would be a serious violation of privacy,” Lina Rosengren-Hovee, an infectious diseases fellow at the University of North Carolina Chapel Hill who has studied the use of Grindr to advertise self-test HIV kits, told Vox. “Discrimination and stigmatization based on HIV status is a very real issue for those who are HIV-positive, and this breach of confidentially can only worsen this problem.”

The independent Norwegian research nonprofit SINTEF first identified the problem. In an analysis of privacy leaks and data sharing at Grindr, SINTEF found that the company is also sharing other personal details of users — including GPS position, sexuality, and phone ID — with a slew of marketing and advertising companies. “And this information, unlike the HIV data, was sometimes shared via ‘plain text,’ which can be easily hacked,” Ghorayshi and Ray wrote.

Justin Lehmiller, a sex and psychology researcher at the Kinsey Institute, was not surprised by the news, given the recent Cambridge Analytica scandal at Facebook. But “this is a different breach of user trust than anything else I’ve seen recently because it involves sharing sensitive health information along with identifiable data,” he said.

Sharing STD information is dangerous not just for the people who risk having their personal data exposed, he added. “There’s also a concern that if users of these apps begin to question whether it is safe to share information about their HIV status, they may be less likely to reveal it, which could potentially create more opportunities for STIs to spread.”

Health officials across the US have linked the recent uptick in STDs to the growing popularity of internet dating (and hookup) apps like Tinder, Grindr, and OkCupid.

They also pretty uniformly agree that these sites and apps could play an important role in preventing STD outbreaks. As I’ve reported, apps can help urge users to get tested at regular intervals anddisclose information about their STD status to their sex partners, and can distribute information about STD clinics and condoms.

But the revelations reported by BuzzFeed may hamper these efforts — at a key moment in the increasingly urgent fight against STDs.

The use of dating apps has been linked to an increased risk of STDs

Though it might seem dating apps are no more to blame for disease spread than the advent of the telephone or proliferation of the bar, researchers have found there is a correlation between online dating and a heightened risk of STDs.

One of the best studies on the sex lives of dating app users, led by Lehmiller, suggests they tend to have more sexual partners than non-app users. That means people who are drawn to apps may just be more sexually active than non-users.

“It may not be that the technology is increasing the risk, but rather there’s this selection effect for people who are more sexually active who tend to use the apps,” Lehmiller told Vox last fall.

Whatever their role, dating apps and sites appear to be helping to facilitate connections — and disease outbreaks — that may not have otherwise happened. And this is especially significant given that a number of dangerous STDs have come roaring back in the US.

According to a September 2017 report from the Centers for Disease Control and Prevention, more than 2 million cases of chlamydia, gonorrhea, and syphilis were reported in the United States in 2016 — the highest cumulative number ever recorded.

Major dating networks like Tinder and Grindr have been slow to respond to these epidemics, but a number of other sites have been moving ahead.

The gay men’s social network Hornet has long allowed users to indicate their HIV status in their profiles, choosing from five options: negative, negative on PrEP (the pill to prevent HIV), positive, positive undetectable, and don’t know. Daddyhunt, another gay men’s dating site, created public service announcements about PrEP, STD testing, and condoms that pop up when users are online.

Grindr, which boasts more than 3 million daily users, had been criticized for its sluggishness in promoting public health. But last fall, Grindr added HIV status and “last test date” as standard fields on its dating profiles. And just last week, the company announced it would regularly remind its users to get tested for HIV.

Now, the revelations about data sharing may make users wary of disclosing that information.

“I’m concerned that this would undermine years of efforts to promote people recording their HIV status in their profile, and sharing their status with others to promote safer sex,” said Jeffrey Klausner, a professor of medicine and STD researcher at UCLA. “Any time anyone feels their information is not secure or is used accidentally, it undermines their perception of the security of their information.”

For those who want to minimize their privacy risks, other companies have already popped up to offer people a secure way to share information about STDs. The Safe app, for example, purports to allow users to share verified information about their STD status from labs where they’ve been tested as securely as their banking information.

The app was a response to the “increased use in dating apps, increases in STDs and HIV, and [concerns about the] security of that particular information,” Klausner said. And it might be one of the places online daters turn to as privacy concerns grow.

“It’s the world we live in,” Klausner said. “[There’s] a trade-off between something the apps and sites offer — which is a great way for people to connect — but unfortunately, we are learning about the potential risks.”