Zaufana Trzecia Strona, a local Polish news site, first reported the attacks late Friday, last week. The news site said that during the past week, the security teams at several, yet unnamed, Polish banks detected downloads of suspicious files and encrypted traffic going to uncommon IPs situated in many foreign countries.
As employees at different banks started looking into their systems, they found malware installed on numerous workstations and even some servers.
Subsequent investigations and a cooperation between different banks eventually discovered the source of the infection as being the official website of KNF, which, ironically, is the regulating body that keeps an eye out for the security of financial systems in Poland.
According to Zaufana Trzecia Strona, this malware has a zero detection rate on VirusTotal and appears to be a new malware strain, never-before-seen in live attacks.
KNF's staff have cleaned their site and along with the affected banks, have reported the incidents to CERT.pl. They also released a statement acknowledging the website hack on Friday, but haven't provided other details about the attack.
The affected Polish banks said the malware that infected their computers and servers encrypted its outgoing traffic and they weren't able to tell what the attackers stole.
Banks reassured their clients and said they haven't detected any unauthorized transactions, but only the mysterious outgoing traffic.
Local media believes the attack is the work of a foreign intelligence agency. A more believable theory would be that this is the work of one of the many cyber-crime syndicates specialized in cyber-thefts from financial institutions.
The attacks have the signs of classic network reconnaissance operations, where hackers gather intelligence in order to create a map of a victim's network before launching their final assaults.