On Thursday morning, Moscow’s busy Fili district became the site of a traffic jam unlike any before it. Motherboard (via The Verge) reports hackers used Russia’s Yandex Taxi ride-hailing app to order dozens of drivers to coverage on Kutuzovsky Prospekt, one of the city’s main thoroughfares. The act caused traffic on part of the already congested street to come to a standstill for about 40 minutes while Yandex worked to address the situation.

“On the morning of September 1st, Yandex Taxi encountered an attempt by attackers to disrupt the service — several dozen drivers received bulk orders to the Fili district of Moscow,” a Yandex spokesperson told Motherboard. In a separate statement shared with Russia’s state-owned TASS news agency, Yandex said it reworked its routing algorithm following the attack to prevent similar incidents from occurring in the future. The event is one of the first known instances of hackers exploiting a ride-hailing app to create a traffic jam.

Several Twitter accounts claiming affiliation with Anonymous say the hacktivist collective is behind the incident. On Friday, one Anonymous account said the group worked with the IT Army of Ukraine, a volunteer organization formed at the start of the war, to carry out the attack.

Anonymous previously claimed responsibility for a cyberattack that took down multiple Russian government websites, including those belonging to the Kremlin and the Ministry of Defence. “Faced with this series of attacks that Ukraine has been suffering from the Russian dictator Vladimir Putin, we could not help but support the Ukrainian people,” the group said at the time.

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