“We know the government is using all kinds of data and trails to charge people later on,” said Lokman Tsui, a professor at the School of Journalism and Communication at the Chinese University of Hong Kong.

Protesters used some of the same tools to organize in 2014, when the Occupy Central demonstration shut down parts of the city for more than two months. But their caution shows a growing awareness that the new digital tools can be a liability as well as an asset.

The police during the Occupy protests used digital messages to justify the arrest of a 23-year-old man, saying he used an online forum to get others to join in. One message that then spread over the WhatsApp chat service included malware, disguised as an app, that appeared to be for eavesdropping on Occupy organizers. Researchers said the malware most likely came from China’s government.

“People are minimizing their footprints as much as possible,” Dr. Tsui said. “In that regard, it’s very different from five years ago. People are much more conscious and savvy about it.”

This week’s protests were sparked by the Hong Kong government’s plans to enact a new law that would allow people in the city to be extradited to mainland China, where the court system is closed from public scrutiny and tightly controlled by the Communist Party. On Thursday, city officials delayed plans to consider the legislation.

Telegram said on its Twitter account that it was able to stabilize its services shortly after the attack began. It described the heavy traffic as a DDoS attack, in which servers are overrun with requests from a coordinated network of computers. In his tweet, Mr. Durov said the attack’s scale was consistent with a state actor.