The Won Collapse
There are several reasons for this decline. First, the sharp increase in the cost of imported oil has wiped out South Korea's previous trade- and current account surpluses. This means that after having previously been able to manage a net capital outflow, Korea must now attract a net capital inflow, which for the reasons described below has been easier said than done.
Secondly, as is reported in this post on the naked capitalism blog, there are increasing worries about the quality of Korea's foreign reserves. The Bank of Korea has much of its reserves in Mortgage backed securities issued by Fannie Mae and Freddie Mac, and so the increasing market distrust of the value of these securities are also increasing market distrust of the won.
And the bearish sentiment created by these events are further eroding market confidence in the won and by extension won denominated assets, creating a self-reinforcing vicious spiral of the kind I explained here.