The main opposition People Power Party (PPP) claimed Thursday it has detected suspicious opinion rigging attempts against its presidential candidate Yoon Suk-yeol as it plans to lodge complaints with election and law enforcement authorities over the issue.

The PPP said it found signs of illicit cyber operations targeting Yoon through its self-developed software Kraken. The software was designed to spot manipulative online comments in order to prevent incidents like the 2017 opinion rigging scandal, in which supporters of the ruling Democratic Party (DP) tried to influence online public opinion ahead of the presidential election.

Rep. Lee Young, who heads the digital unit of the PPP's election committee, said the unit found online comments that are believed to be posted systemically with an intent to slander Yoon.

Lee said malicious comments containing the same message were uploaded repeatedly through various user accounts, with only small changes, such as adding different emojis, made to the original comment defaming Yoon.

The lawmaker also said there were signs of deliberately jacking up the number of "likes" on political comments in favor of the DP and its presidential candidate Lee Jae-myung.

"We cannot decide whether it was done through a software macro, but its pace of increasing the number of likes appears to be the result of an organized move and is also beyond the normal level," Lee said.

Using the Kraken software, the PPP screened some 350,000 online comments first and determined that at least 964 comments were written in an organized scheme to harm Yoon's campaign, according to Lee.

After reviewing legal matters, the PPP said it will notify internal portals and then file complaints with the election watchdog and investigative authorities. (Yonhap)