Mastodon’s flagship server was hit by a distributed denial-of-service attack on Monday, the social networking software maker said, which rendered the instance unusable at times. Much of the site was inaccessible, throwing error messages or displaying a full-screen outage warning. The makers of the decentralized social networking software, which runs its official mastodon.social instance, said in a status update at around 7 a.m. ET on Monday that it was investigating the cyberattack. By 9:05 a.m. ET, Mastodon said it implemented a “countermeasure against the DDoS attack, and the site is accessible.” However, the company warned that some instability may continue to be seen as the attack is ongoing. The cyberattack targeting Mastodon comes days after Bluesky, another decentralized social network, resolved much of its days-long outages following a lengthy DDoS attack. As of Bluesky’s upd a te on April 17, the DDoS attack continues, but its service has been stable since April 16 at 9 p.m. PDT.…