Blog service LiveJournal.com, which has been down for much of this week, admitted Wednesday that the problems were caused by hacker attacks, not technical malfunction.

The DDoS attacks targeted the company’s Internet service providers in the United States, Qwest and Verizon, taking them down for about five hours on Monday, Ilya Dronov, development director with the site’s owner, SUP, wrote on his blog. The attacks continued Wednesday, he said, without specifying who might be behind them or when they would be resolved.

An attack of this scale costs about $15,000 to organize, Gazeta.ru said.

It is the third such attack on LiveJournal, which is the main platform for political dissent in Russia, since March. Previous attacks targeted popular bloggers, including whistleblower Alexei Navalny, which led to speculation that pro-Kremlin groups might be involved.