The Czech Republic has been hit by an unprecedented wave of cyber attacks this week, with investigators stumped over their origin amid concerns they could lead to worse mayhem.
"We don't know anything about the motivation for now, because no one has claimed the attacks," National Cyber Security Centre spokesman Radek Holy said after attacks on media, banks and telecommunications websites. "The character of the attacks gives us absolutely no clues about the reasons."
Hackers on Monday launched a DDoS (distributed denial of service) attack on leading Czech news websites, blocking their servers with hundreds of thousands of requests. On Tuesday, they targeted Seznam.cz, the most popular Czech search engine, then on Wednesday took on the Prague Stock Exchange, the central bank and several commercial banks, before attacking two national mobile-phone operators on Thursday.
According to Karel Kucharik, head of the country's police cyber-crime squad, this week's assault constituted "the biggest attack of its kind in the Czech Republic since the internet was launched".
Hany Farghali - spokesman for Telefonica Czech Republic, whose website was among those targeted - said the internetprovider (IP) addresses behind the attacks were Russian.
"I can confirm that we are co-operating on the international level," Czech police spokeswoman Marketa Johnova said, without disclosing details "for tactical reasons".
However, Holy was sceptical about the Russian link.
"We definitely can't say this attack has come from Russia. The IP addresses are not only Russian, they are from other parts of Europe, too," he said, explaining that the attackers were taking control of drone computers. The computers' "owners may not even know about it".
Hackers on Wednesday led an assault on major banks including Ceska sporitelna, owned by Austria's Erste Bank; Komercni banka, owned by France's Societe Generale; CSOB, which is in the hands of Belgium's KBC; and the local branch of Austria's Raiffeisenbank.
Czech media were awash with speculation the following day. They suggested it was work of a solitary hacker looking to boost his ego, or a protest movement similar to Anonymous, or a test ahead of a more serious assault.
Holy said this was "a possibility which is however impossible to confirm".