Lacoon Chief Executive Michael Shaulov told Reuters that Xsser is the most sophisticated malware used to date in any known cyberattack on iOS users.

"This is one the most interesting developments we have seen," he said. "It’s the first real indication that really sophisticated guys are shifting from infecting PCs or laptops to going after iOS devices."

The code used to control that server is written in Chinese. The high quality of the campaign and the fact it is being used to target protesters suggests that it is coming from a sophisticated attacker in China, Shaulov said.

"It is the first time in history that you actually see an operationalized iOS Trojan that is attributed to some kind of Chinese entity," he said.

A Trojan is a term used by cyber researchers to describe malware that enters a device disguised as something harmless.

Still, he said that his company’s research team has yet to identify any specific victims of the iOS Trojan.

Lacoon said on its blog that it is possible the attackers might have deployed the Trojan in other places, in addition to spying on pro-democracy protesters in Hong Kong.

"It can cross borders easily, and is possibly being operated by a Chinese-speaking entity to spy on individuals, foreign companies, or even entire governments," they said in a blog post describing their analysis.

FireChat, launched only in March this year, allows smartphone users to communicate via Bluetooth or WiFi, an alternative to cellphone networks. Its chat-rooms, dubbed “firechats”, allow users to communicate without exchanging data with traditional cellular networks. These live and anonymous discussion groups can gather as many as 10,000 people simultaneously, according to Open Garden.

Additional reporting by James Griffiths