Banks and other financial institutions in South Korea have been on guard over threats of cyberattacks by alleged financial blackmailers, according to the banks and financial institutions on Tuesday.

No damage has been reported so far, but about 20 banks, brokerages and the Korea Exchange received threats by hacking groups about paralyzing their Web sites.

They received e-mails that set a deadline to transfer funds to the blackmailers to avoid the attacks. 

On Monday, four financial institutions -- the Korea Financial Telecommunications & Clearings Institute, Suhyup Bank, DGB Daegu Bank and JB Bank -- came under a distributed denial of service attack by a hacking extortion group named "The Armada Collective."

The four institutions, however, fended off the attacks, according to officials at the Financial Supervisory Service.

Banks and financial institutions have been beefing up protection for their systems.

Kookmin Bank has set up an emergency response team against cyberattacks, while KEB Hana Bank has raised its alert status against cyberattacks by one notch.

The Bank of Korea was also on alert earlier this month after activist hacking group "Anonymous" warned that it will wage cyberattacks against central banks around the world.

The central bank has reported no attack from the group so far. (Yonhap)