I would be surprised by an Al Qaeda terrorist attack in South Korea, but without a doubt some bad actors have transited or had prior plans to attack South Korea:

Since the recent suicide bombing in Yemen that killed four South Korean tourists, the nation’s intelligence agency is watching closely 105 foreign passport holders for possible terrorist-related activities, a report by the nation’s spy agency submitted to the parliament showed Saturday.

Among the 105 foreign nationals, those from the Middle East topped with 87, followed by 10 from Africa and the rest from Asia and the Pacific regions, Yonhap said Saturday.

The National Intelligence Service is closely watching them and cooperating with intelligence bodies in other countries to collect additional information on them.

The intelligence body is particularly paying attention to those foreign individuals with suspected ties with al-Qaida and is checking their entry to and exit from the country.

An unnamed lawmaker who is on the National Assembly’s intelligence committee said, “There are quite a number of foreigners in South Korea who are suspected to have ties with terrorist activates. With the Yemen incident, it is my understanding that the authorities ramped up its watch on these individuals.”

Meanwhile, the government designated all of Yemen as a “travel restriction area,” asking people not to travel to the Mideast country.  [Korea Times]

Some may remember Al Qaeda 9/11 mastermind Khalid Sheikh Mohammad actually planned to conduct terrorist attacks against US military targets in South Korea:

I was responsible for planning and surveying to hit American targets in South Korea, such as American military bases and a few night clubs frequented by American soldiers.

Al Qaeda’s number two leader, Alman al-Zawahiri has also expressed an interest to attack South Korea as well as a Al Qaeda linked Jemaah Islamiah cell being broke up a few years ago within Korea that led to a Korean-American Islamist receiving a 11.5 year prison sentence back in the US after he was deported from Korea.

I have always felt that if Al Qaeda was going to strike Korea they would target the subway system.  As past Al Qaida attacks have shown they like to attack soft mass transit targets and Korea’s mass transit system is a big soft target that has the potential for many casualties which was evident by the 2002 Taegu subway fire which killed 130 people.  This tragedy could unfortunately be a blueprint for a future Al Qaida attack, which I think Korean authorities have been working hard to prevent.