The explanation of all the opcodes for the contact script does not list any IO operations for external (non-storage) data (at least none that I could see). However, in the list of Ethereum examples, the following is given:

"Crop insurance. One can easily make a financial derivatives contract but using a data feed of the weather instead of any price index. If a farmer in Iowa purchases a derivative that pays out inversely based on the precipitation in Iowa, then if there is a drought, the farmer will automatically receive money and if there is enough rain the farmer will be happy because their crops would do well."

Does somebody know how the contract would be able to read a data feed? I did not find anything in the language spec. Such a feature would be really interesting. On the one hand it would allow for a ton of interesting options (binding contracts to stock markets, emails, political events) on the other hand how would a contract behave if the required data url is gone (i.e. the weather data feed changed from weather.php?v1 to /v1/weather). Whats more, wouldn't there be strong incentives for man in the middle attacks to deliver wrong data? This sounds like a very powerful yet dangerous feature, so I'd love to learn more about the spec and reasoning behind this.