Computer servers of South Korea’s top broadcasters and major banks fell victim to apparent hacking attacks on Wednesday, raising speculation that the intrusion came from North Korea just days after it blamed Seoul and the US of waging cyber war.

Yonhap news agency quoted an unnamed official from South Korea’s presidential office as saying the attacks were traced back to North Korea, through a Chinese IP address.

The attacks brought down the network servers of television broadcasters YTN, MBC and state-controlled KBS as well as two major commercial banks, Shinhan Bank and NongHyup Bank, reports Reuters.

Screens went blank on Wednesday afternoon, with images of skulls reportedly popping up on the screens of some computers. The breach affected about 32,000 computers, paralyzing operations in banks and TV networks, according to the South’s state-run Korea Internet Security Agency.

Shinhan Bank reported a system shutdown, affecting online banking and ATMs. The bank also couldn’t conduct any customer activities at bank windows, including retail and corporate banking, according to The Associated Press.

Broadcasters KBS and MBC said their computers went down around the same time, but officials said TV broadcasts were not affected. YTN cable news channel said the company’s internal computer network completely blacked out.

“Their computer systems were infected with a malignant code. So we can say that there was a hacking attack,” said Shin Hong-sun, an official at the Korea Communications Commission, which overseas telecoms and broadcasting.

Massive cyber intrusions take at least one to six months of planning and coordination, according to Kwon Seok-chul, chief executive officer of Seoul-based cyber security firm Cuvepia Inc.