Demonstrators gather at Argyle Street and Nathan Road in the Mongkok area in Hong Kong on Monday.  (Brent Lewin/Bloomberg)

In the heart of Hong Kong, where the largest pro-Democracy protest to challenge Beijing since the 1989 Tiananmen Square gathering has been brewing, some protesters are reportedly turning to a mobile app that lets users create their own networks to communicate. But those networks lack basic security protections.

The app, called Firechat, relies on the principal of mesh networking. It works by creating a sort of daisy-chain between devices using Bluetooth or WiFi capabilities, allowing for people in the same area to connect directly with one another or band together to cast a wider net. The developer, Open Garden, advertised the app as a way to connect to others nearby when off the grid -- such as when at the beach or camping -- or in more connected areas.

But in areas facing civil unrest where protesters worry about Internet access being cut or are battling against overwhelmed cell towers, the app has seen surges in popularity.

Between Sept. 9 and Oct. 4, the app was downloaded 460,000 times in Hong Kong, according to Open Garden chief marketing officer Christophe Daligault. The company also observed 5.1 million chat sessions in the region, Daligault says, but notes that the service can't track the number of chat sessions that take place exclusively through locally created networks.

Firechat only launched in March, but this isn't the first time it has been deployed in a protest environment: Taiwanese students reportedly used the app while protesting a trade agreement with China in the spring, according to NPR, using the mesh networking capabilities to combat weak or nonexistent cell coverage. But the surge in Hong Kong is many times larger than the protests in Taiwan, according to Daligault.

A local student activist leader, Josh Wong, took to social media to advise protesters to download the app in case cell service was taken down in the early days of the protest. There haven't been reports of Internet service or cell towers being down in Hong Kong, but some online services have been censored in China. Instragram was blocked in the Chinese mainland, and there were some signs that photos related to the protests were being deleted or blocked on some Chinese social media services. Some reports also suggest there has been shoddy cellular service in protest areas because of the massive crowds of people.

"Cellular networks are overwhelmed," says Daligault, "but those are situations where our network shines -- because the more devices that are connected, the more resilient our network becomes."

He says the company doesn't know what is said in any off the grid conversations in Firechat, so he can't be sure how much actual organizing may be occurring via the chat app. Washington Post correspondents on the ground reported Firechat wasn't being used as an essential organizing tool. Rather, they said, it was downloaded as a backup, and other services with larger built-in audiences, including WhatsApp, were more common.

Users may have reverted to more familiar apps after testing out Firechat. The app can be a bit overwhelming -- when launched the first time, a giant chatroom appears with a firehouse of comments. Also, the mesh networking components may be tricky to configure. Tech reporters at The Post were unable to get the app to work outside of a traditional cell network within the office, despite testing it with a variety of devices.

And then there's the security aspect: In WhatsApp, users can create private lists and groups. But everything said on mesh networks created using Firechat is public, even if in smaller chatrooms. There's also no encryption, which means that anyone nearby could potentially eavesdrop on activists' conversations by either joining the network in the same geographic area or using antennas.

Daligault says users' messages and usernames are transmitted. The company always advises those using the app in protest scenarios to be aware that content is public and to use pseudonyms -- something Chinese Internet users are already likely to do because of restrictions around online speech.

The app was designed to connect people, Daligault says, but not necessarily to do so securely, and the company is very aware of its drawbacks. Those drawbacks aren't unique to Firechat but are an issue that mesh networks across the board struggle with, says Josh King, lead technologist at New America's Open Technology Institute, which has it's own mesh networking project called Commotion.

"Mesh networking introduces a lot of potential security challenges, none of which are impossible to overcome," King says. "But generally when you are trading a centralized system for a decentralized system you're trading that resiliency for additional complexity." And with greater complexity comes greater security challenges.

"The challenge comes in because essentially the traffic for any one person has to pass through every intervening device to get to the recipient," King explains, so one bad actor who joins in a network may potentially spy on a significant portion of the network.

But there are benefits to mesh networking during protests. The resiliency of mesh networks means that if official infrastructure fails there are backup layers of communication. And if the official infrastructure is already being snooped on, mesh networking alternatives may even seem safer.

"One of the main appeals of a network like this is that it's separate from main structures -- it provides a separate channel of communications," albeit one potentially easily compromised, says King.

William Wan and Ishaan Tharoor contributed to this report.