Hackers are targeting major commercial banks in the Czech Republic, bringing down their website and affecting their online banking.
The websites of the country's central bank and the Prague's Stock Exchange were also not accessible Wednesday morning.
Pavla Havova, spokeswoman for the CSOB bank, which belongs to Belgium's KBC, says the bank's website and its Internet banking are affected by Wednesday's attack.
The other major banks, including the Czech branches of Austria's Erste Group and France's Societe Generale say they have also been affected by the denial of service attacks, a technique that works by overloading a website with online traffic.
The banks say their clients' data and deposits are safe.
The attacks came two days after leading media websites in the Czech Republic also faced cyberattacks.