Hackers attacked the websites of the Czech central bank, several top commercial banks and the Prague Stock Exchange on Wednesday, slowing or shutting down online services in the latest in a series of such attacks across Europe in recent weeks.
The attacks, caused by flooding systems with digital requests that overwhelm servers, followed a wave of assaults on the Czech Republic's main news websites on Monday and Tuesday.
The largest Czech bank, CSOB, said the cyber attack which disabled its online services in the morning had come from abroad.
The website became operational again after CSOB blocked access to it from countries from which the attack came, it said, without disclosing which countries those were.
The online banking sites of Erste Group Bank's Ceska Sporitelna, Societe Generale's Komercni Banka and some smaller banks also suffered attacks that shut down their internet banking and other online services.
The website of CSOB's sister bank in neighbouring Slovakia was also hacked but was functioning as normal later in the day, spokeswoman Zuzana Eliasova said.
The Czech central bank website used for public announcements and the release of economic data was hit, but no such announcements were due, spokesman Marek Petrus said.
Prague Stock Exchange spokesman Jiri Kovarik said the bourse's web site was attacked in the morning and its functioning was later renewed. "Most likely it was part of some coordinated attack by hackers," he said.
The attacks against top Czech news websites earlier this week, which slowed or crashed their home pages, was the latest in a series of cyber assaults on media outlets around the world.
Campaign group the Committee to Protect Journalists said last month attacks on media organisations were on the rise and hackers were being hired to target reporters and websites by bodies trying to censor news outlets.
The New York Times and the Wall Street Journal have both said that cyber attacks targeting them in January originated in China.
In a separate and potentially more damaging spate of attacks in recent weeks, hackers targeted dozens of computer systems at government agencies in the Czech Republic, Ireland, Romania and other European counties, exploiting a security flaw in Adobe Systems Inc's software, researchers said last week.
That attack could have siphoned off data from infected computers.
Romania's security service said it believed another state was behind that attack, dubbed "MiniDuke", that hit its national security institutions as well as NATO. It did not name the state.
Get all the latest news and videos in your inbox. Register FREE