Prosecutors said Wednesday they have summoned ruling Grand National Party (GNP) lawmaker Choi Gu-sik as part of their ongoing probe over the controversial hacking of the country‘s election watchdog in October.

The two-hour attack paralyzed the web sites of the National Election Commission and Park Won-soon, a leading Seoul mayoral candidate, during the Oct. 26 by-election for the mayoralty and other governmental posts. Park was elected mayor despite the attacks.

Choi, a two-term GNP lawmaker, was summoned to testify whether he was aware of his former aide’s involvement in the attack. He entered the prosecutors‘ office with his attorney at around 7 p.m.

The summons comes after the GNP, which is stepping up reform efforts, decided to recommend Choi to voluntarily give up his party membership. The GNP plans to sue any party officials found to have been involved in the hacking.

The 27-year-old former aide, identified by his family name Gong, is alleged to have masterminded the hacking with the former secretary of National Assembly Speaker Park Hee-tae and ordered a 25-year-old chief of a local information technology firm to carry out the attacks.

Amid growing calls to investigate any potential involvement of ranking GNP lawmakers, prosecutors confirmed in mid-December that the ex-secretary of Park, formerly affiliated with the ruling party, had transferred 100 million won ($86,505) to suspected hackers. (Yonhap News)