Note that KT, while relatively recently privatized, is still a national corporation that is considered a critical national asset under the law (thus if the North attacks, KT towers are first priority to be protected by the South's military). So, it is not as if some rogue SME infected its users with malware; it's a national corporation infecting its users over and not even be sorry about it (as in the article).
Plenty of other comments detail the strange Active X requirement: The national law had dependency on Internet Explorer/Active X. (I do not know of any developed nation having a national legal dependency on a specific corporation's consumer technology at this scale.) Also, many comments on South Korea's purportedly great infrastructure (albeit two decades ago). There is more to this.
Interestingly, if you ask an average Korean, he would say Korea is literally the best nation in IT/internet technology, topping or at least on par with the US. The national propaganda effort that went into forming this collective conscious should not be understated. Even many of the top programmers in South Korea I met strongly believe in this superiority. I wonder if this strong sense of superiority is both (1) preventing SK from improving its actually-lagging tech and (2) act in Dostoevskian-Raskolnikov manners thinking that it is above the law and consensus ("the best can break the rules and set new ones"). Whatever the underlying reason may be, there is a serious techno-cultural issue going on in the country.
One of the biggest banks in South Korea blacklisted Amazon as a financial scammer because it's Prime subscription renews monthly and customers complained after seeing the renewal charge on their credit cards. The ban was national -- no customer of this bank could buy a product from Amazon unless he calls the bank personally and ask the charge to be approved. Again, the issue wasn't technical. It was cultural.