Although the attack in Paris on the satirical magazine Charlie Hebdo has been widely condemned online, some people have praised the violence.
The top 10 trending hashtags in English and French on Friday included "CharlieHebdo, #ParisShooting and #JeSuisCharlie.
But hashtags in Arabic supporting the attackers also proliferated, including #TheLoneWolvesTerrifyFrance, #I_Am_A_Muslim_The_Charlie_Incident_Represents_Me and #ParisIsBurning.
On Friday, Tharwah Mowahed tweeted in Arabic that he looked forward to similar attacks on American soil.
"You who put joy in our hearts by igniting the Paris fire, make us happy with flames in America, to see what they will do. :)," he tweeted under the #ParisIsBurning hashtag.
Bint Abdullah tweeted in Arabic that the attack was a payback for the mistreatment of Muslims in France:
"France is the country that openly hates Islam they banned the honor of the Muslim women have you not seen how they treat our sisters," she wrote.
Asil Baghdadi joined the Hashtag campaign #I_Am_A_Muslim_The_Charlie_Incident_Represents_Me, tweeting his support for the gunmen on Friday.
"Every attack in which the enemies of Allah and His Messenger are killed represents me. I'm with terrorism," he wrote.
IvanIS wrote that the attack was retribution for Charlie Hebdo's cartoons mocking the prophet Muhammad, and French tolerance of such speech.
"Paris got a wake up call! Cartoonists wish to mock Islam got what they deserved! Don't fight against Islam n expect roses in return," he wrote.
Abu Suleyman tweeted that the attack should send a message not just to France, but to all Western countries.
"The #ParisShooting is directed at Western protection of criminals who insult the Prophet, #CharlieHebdo is meant to be an example," he wrote.
Hajer, another supporter of the shooters, tweeted that he hoped the attack would have a chilling effect on free speech.
"Because of the lions in Paris, no newspaper will dare to curse our beloved and our example Mohammad the Messenger of Allah," he wrote.
Some praised the attackers online via multimedia posts, including the post-apocalyptic image of a fighter from the video game "The Line" with an Islamic State stamp superimposed on his mask under the headline, "ISIS are Everywhere #Charlie Hebdo"
Muslim extremists also attempted to nullify the #JeSuisCharlie hashtag by tweeting a picture of it with a red slash replaced by "Je suis Muslim," spelled in a mix of Arabic and French and paired with an admonishment to those who would insult the prophet Mohammad, "no matter who they may be."
Another picture, tweeted by the group "Victory for the People of Tawheed," showed victims of the Charlie Hebdo attack beside silhouettes of Islamic State fighters and a flag bearing the Islamic shahada, or statement of faith, and the seal of the prophet.
Abu Umar Fateh uploaded a compilation of video of the attack.
Some groups encouraged future lone wolf attacks by young Muslims in Western countries.
Ehsanullah Ehsan, spokesman for the Jamat-ul-Ahrar group in Pakistan, praised the attack and congratulated its organizers.
"We r delighted to hear about attack on evil team of Charlie Hebdo.... May Allah grant the Mujahideen of Paris attack highest status in paradise," he wrote.
Others also warned of future attacks.
"Congratulations to France and its people for harvesting what their hands have sown. Do those malicious artists think we are a nation that remains silent to those who mock our Messenger, Allah's peace and blessings be upon him?" wrote a member of the pro-Islamic State Minbar Jihadi Media forum.
"Does Hollande and whoever preceded him of governments think that their interventions and their plotting against the Muslim countries will pass without punishment?" he said of French President Francois Hollande.
"No, by Allah. The youth of Islam will not remain silent from now on, especially now that we have a State that will prepare armies if someone touches one from the Ummah of Islam," he wrote, referring to the Muslim people.