The Tokyo Metro Co. and Osaka Metro Co.'s websites were rendered inaccessible on Wednesday evening in what appears to be a second day of cyberattacks on Japan, with a pro-Russia hacker group claiming responsibility on social media.
The attacks, which may have been perpetrated by Killnet, come a day after the group claimed responsibility for assaults on Japanese government websites.
At around 6:30 p.m. on Wednesday, Killnet wrote on messaging app Telegram that it had declared war against what it called Japan's anti-Russian campaign, and also uploaded a video. Shortly after at around 7 p.m., the group posted again claiming it would stop Tokyo's subway network.
The latest disruption appears to have been caused by another DDoS attack, in which a network is overwhelmed by hackers sending floods of data from multiple sources over a short period.
The government websites affected on Tuesday, including the e-Gov web portal, appears to have been hit by a similar strike, which impeded access to its services.
Access to 23 websites across four government ministries was disrupted, Chief Cabinet Secretary Hirokazu Matsuno told a Wednesday press conference. He also noted that the websites had returned to functionality and no data leaks had been confirmed at the time.
On Tuesday, Killnet posted on its Telegram claiming responsibility for the attacks and appeared to write that it was revolting against Japan's "militarism" and kicking the samurai.
Matsuno said regarding the group's claims that it had staged the attacks that he was aware they had implied responsibility, but only went as far as saying that "the cause of the disruption including its connection (to Killnet) are in the process of being confirmed."
Killnet are believed to have been behind a number of cyberattacks on websites belonging to countries supporting Ukraine following Russia's invasion of it.