MANILA — Hundreds, if not thousands, of Philippine journalists and students awoke Sunday to find Facebook accounts made in their names — mostly ghostlike profiles with few or no friends, no pictures and sometimes misspellings.

Some accounts blocked the people they sought to imitate. Others signaled an intention to impersonate the genuine accounts. By evening — after Facebook announced an investigation — the trolls attacked.

“You son of a b---- terrorist,” one fake account told a student at the Polytechnic University of the Philippines, before threatening sexual violence.

The Catalyst, a campus publication, documented menacing messages sent to at least 15 students from their corresponding dummy accounts. The messages included death threats and accusations that students were communists, said Dominic Gutoman, the editor in chief. His staff also found their names used on fake accounts, which he said “cast a chilling effect on our campus journalists.”

The attacks — widely viewed as the work of troll farms, where staff for hire spend full shifts defending their clients and disparaging rivals — marked a grim new development in the Philippines’s dystopian Internet landscape.

They were also the latest controversy involving Facebook, which has faced criticism that its platform amplifies disinformation and hate speech, resulting in a corrosive effect on democracy. In the Philippines, the populist leader Rodrigo Duterte has admitted deploying online trolls during his successful presidential campaign in 2016.

Last month, Facebook appointed an oversight board to rule on “difficult and significant content decisions,” it said in a statement. Facebook chief executive Mark Zuckerberg on Saturday posted a seven-point response to the recent controversy, saying the company would review its policies on threats of state use of force and on content violations.

The dummy profiles — which some users have labeled “clone” or “shadow” accounts — have materialized at a fraught moment in Philippine politics. Duterte is poised to sign contentious anti-terrorism legislation that expands the definition of terrorism and that experts say will enable his administration to crack down on government critics. The measure’s recent passage through the legislature triggered protests, resulting in the arrests of at least seven people in the central city of Cebu.

Some opponents of Duterte have speculated that the accounts are meant to intimidate them into silence, or that they are being saved to plant evidence against those critical of the government. In recent months, civilians have been summoned by government investigators for their Facebook posts, while others have been arrested and charged with sedition or spreading false information about the government’s response to the coronavirus pandemic.

The National Union of Journalists of the Philippines said that as of Monday, it had recorded more than 700 cases of dummy accounts, mostly affecting media workers. A newly founded Facebook group dedicated to helping users report fake accounts racked up more than 5,000 members.

Facebook said Sunday that it was looking into the matter, but it did not provide further updates. It encouraged users to continue reporting suspicious behavior.

“The people who engage in this type of behavior are persistent, often well-funded, and constantly evolving their tactics to try to evade our systems,” a Facebook spokeswoman said. “However, our machine learning systems become more efficient and effective with every single account they identify.”

The Philippines’s Justice Department has announced an investigation, while the National Privacy Commission said it was monitoring the situation. Victor Lorenzo, a senior official with the National Bureau of Investigation, the country’s equivalent of the FBI, said that the deluge of empty accounts could have been caused by a glitch.

This assessment was “worrisome,” said Nonoy Espina, the president of the journalists’ union, as “many of the threats are specific to [the] opposition to the anti-terror bill or to the current administration’s governance.”

Justice Secretary Menardo Guevarra said an initial government report is expected in a week. “For now, it’s premature to even speculate” about the origins of the troll accounts, he said in an interview.

According to Facebook, millions of fake accounts are blocked at the time of creation. In the first quarter of this year, 1.7 billion fake accounts were removed globally, more than 99 percent of which Facebook said were taken down before they were reported.

An investigation by The Washington Post last year found that social media giants and troll farms essentially play a game of cat and mouse; as the algorithms change, those manipulating them have to seek new ways to stay on the platform, or exploit other loopholes in the implementation of community standards.

Macky Del Rosario, a 28-year-old publicist, shared on Twitter a private message sent from his duplicate account. After a string of curses and a death threat, the person managing the fake account said, “Your reporting us will lead nowhere.”

Del Rosario said that should have made him want to be less vocal about his politics — but it only made him angrier.

“I believe more than ever we shouldn’t let fear get in the way of using our voices and taking steps toward progress for a better country,” he said.