Bluesky said late last week that a widespread outage affecting its social media platform was caused by a “sophisticated” distributed denial-of-service (DDoS) attack that disrupted several core features of the service.

The decentralized social network said the incident began on April 15, when the company received reports of intermittent outages affecting the app. Bluesky said its engineers worked overnight to mitigate the attack, which intensified throughout the day and affected feeds, notifications, threads and search functions.

“The application has remained stable since April 16 despite ongoing distributed denial-of-service (DDoS) attacks,” the company said in a statement on Friday. According to internet monitoring website Downdetector, user reports show no problems with Bluesky as of Monday.

Bluesky said it found no evidence that the incident involved unauthorized access to private user data.

DDoS attacks flood online services with large volumes of traffic, making websites or apps slow or completely inaccessible to legitimate users.

The company has not attributed the incident to a specific threat actor. However, an Iran-linked hacker group calling itself 313 Team claimed responsibility for the attack in a message posted to its Telegram channel last week, saying it had launched a “massive cyberattack” targeting Bluesky’s application programming interface (API).

Bluesky has not publicly addressed the claim and did not immediately respond to a request for comment.

Cybersecurity researchers have previously linked the 313 Team to retaliatory cyber operations that appear aligned with the interests of Iran-backed Shiite militias. The group is believed to operate out of Iraq and typically targets organizations or platforms associated with countries seen as supporting the United States or Israel.

Bluesky has grown rapidly since 2024 as users migrated from Elon Musk’s X following the re-election of U.S. President Donald Trump. The platform now counts roughly 43.7 million users, though it remains significantly smaller than X and Meta’s Threads, which each have hundreds of millions of monthly active users.