Grindr, the world's largest gay dating app, is under fire for allegedly sharing users' HIV status with third-party apps.

The company launched a feature last spring allowing its 3.6 million users to share their status, and last test date, saying it was a bid to destigmatize the disease.

Now, a year later, a report shared with Buzzfeed News reveals those details are being shared with two app-optimization services, Apptimize and Localytics, along with identifiable information such as phone ID, email and GPS coordinates.

It means millions of peoples' highly-sensitive information is far more vulnerable, and at risk of being hacked from any one of the three firms.

While Grindr insists it is standard practice for an app, the news has sent shockwaves through the community, with thousands calling for the app to immediately cut ties with the other firms.

Grindr claims it is standard practice but it has raised questions about privacy and transparency

'The limited information shared with these platforms is done under strict contractual terms that provide for the highest level of confidentiality, data security, and user privacy,' Grindr's chief technology officer Scott Chen said to BuzzFeed News.

The sharing relationship was first spotted by Norwegian nonprofit watchdog SINTEF.

The lead researcher Antoine Pultier told Buzzfeed News users could be easily identified using the information shared: 'The HIV status is linked to all the other information. That's the main issue. I think this is the incompetence of some developers that just send everything, including HIV status.'

Grindr is not selling the personal data, rather sharing it with app-optimization companies to improve the app, learning more about their users and community.

However, it has sparked questions about the firm's dedication to supporting and nurturing an under-served community.

The report comes amid the scandal over Facebook selling personal data to Cambridge Analytica.

Grindr is made for all people who identify as bi or homosexual, but is primarily geared towards men. It is available in every country in the world, including every country with laws that criminalize homosexuality.

The app has fashioned itself as a front runner in the fight to destigmatize HIV diagnosis, prevention, testing and treatment with a number of features allowing users to find testing sites and be open about their status.

Last week, Grindr was lauded for a new feature that will send users reminders to get tested, along with tips of where to find 'non-judgy' doctors.

The move was met with delight from the HIV community, with many hailing it as a 'breakthrough'.

Recent CDC figures revealed HIV infection rates have plummeted among all groups but are on the rise among some groups of gay men, particularly the young and Latino. Since 2008, the overall rate among men who have sex with men (MSM) decreased around 14 percent. Meanwhile, the rate has increased 5.7 percent among gay men aged 25 to 34, and 3.1 percent among Latinos.

To curb the rising rates and to promote safe sex, Grindr created a drop-down menu of options for users to say whether they were positive, negative, on HIV treatment, or on PrEP (pre-exposure prophylaxis, a daily pill to prevent infection). Many doctors hoped this would incentivize more HIV negative users to start taking PrEP, so they could tick that box.

However, privacy advocates and HIV support groups warn today's news may leave users in fear of publicly posting their private health details; it's one thing sharing it on an app used by other gay men, it's another if that information is being passed from pillar to post.