Turkish banks reported sporadic disruption to credit card transactions on Friday as hackers stepped up a two-week barrage of cyberattacks, believed to be the worst the country has seen. Early reports of the assault appeared after various banking institutions were hit on Thursday.
Local media have suggested that the bombardment of public and financial websites could be coming from Russia, after a sharp worsening of tensions between Moscow and Ankara, or staged by the hacking group Anonymous.
On Monday, a video purportedly released by Anonymous declared war on Turkey, accusing it of funding the Islamic State terror insurgency.
"Dear Government of Turkey, if you don't stop supporting ISIS, we will continue attacking your internet, your root DNS, your banks and take your government sites down," the video says, referring to an alternative name for the Islamic State. "We will destroy your critical banking infrastructure."
But no clear evidence of who was behind the assault on Turkey's banks has yet emerged, and authorities have avoided pointing the finger.
Officials at several Turkish banks including Isbank, Garanti, and state lender Ziraat Bank confirmed the attacks, saying they had caused intermittent disruption. Bank shares were unmoved by the news.
"The attacks are serious," said Onur Oz, a spokesman for Internet provider Turk Telekom. "But the target is not Turk Telekom. Instead, banks and public institutions are under heavy attack."
"A majority of Turkish institutions use Turk Telekom as the service provider, therefore we are the ones doing the defense against these attacks," he added.
A government cyber security unit was taking precautions and the situation was under control, Transport, Maritime Affairs, and Communications Minister Binali Yildirim said earlier this week. He did not comment specifically on the targeting of banks, and his ministry was not available for comment on Friday.
On Wednesday, Yildirim criticized the Ankara-based Middle East Technical University (ODTÜ), which operates Turkey's ".tr" domain, over its response to the attacks. The domain includes the web addresses of ministries, the military, banks, and many commercial sites.
"This attack has shown that ODTÜ has not taken the necessary measures," he said. "Such attacks are part of daily life; there could be an attack at any moment from anywhere. So we constantly need to take measures and keep our security level high."
The school quickly defended itself.
"We have faced one of the biggest cyberattacks the world has ever seen and our teams have quickly responded to the threats created by organized groups from outside Turkey," ODTÜ Rector Ahmet Acar said in a written statement.
"These attacks began two weeks ago but have intensified over the past two days," said Burak Atakani, a network specialist from Istanbul Technical University.
He said that the service provider used by some universities, police academies and the research department of the military had also come under attack.
Turkey incensed Russia last month by shooting down a Russian military plane near the Syrian border, and Moscow has retaliated with economic sanctions. In the past, countries such as Estonia and Georgia have suffered cyberattacks emanating from Russia after incurring Moscow's anger.
Reuters sought comment from the Russian foreign ministry, but none was immediately available.
Separately, the Anonymous hacking group posted a video over the weekend on YouTube, which has since been removed, saying cyberattacks would continue if Turkey "doesn't stop supporting" Islamic State.
Some of Ankara's critics, including Russian President Vladimir Putin, have accused Turkey of supporting and aiding Islamic State militants, a charge the government denies.