Managed exchange systems.
Managed exchange systems such as those with a currency peg or those that try to keep a currency within a defined band are potentially vulnerable to speculative attack. All foreign currency transactions have to go through the central bank, which manages its country’s foreign currency reserves. A speculative attack on a US$ base pegged system usually involves borrowing the local currency and selling it to buy US$. This is usually achieved by using the forward markets. Once the central bank runs out of US$ the pegged system is bound to collapse. Speculators do not act alone and do not have to have the financial resources to bet against the central bank, they are more akin to surfers riding a particularly strong wave.