Here is a link to a nice little article on the idea of Interuption Driven Development by Vikas Hazrati at InfoQ: Interruption Driven Development
Vikas discusses the situation where a team needs to work on unplanned bug fixes and other “emergencies” during a Sprint thereby diminishing the value of following the Scrum methodology. Here is the situation he describes:
Scrum talks about having minimum disruptions during the sprint so that the team can work effectively in achieving their target. The Scrum master, is responsible for removing those impediments which might hamper the velocity of the team. However, in a practical situation, when the team is churning out deployable increments of functionality, they have to support production issues along with new feature development. These interruptions, might seem like a disruption to the team but they are important impediments to the system users and the product owner. The product owner, would not see any value in adding new functionality to the system if the existing system is not working fine.
He covers a few approaches to dealing with this scenario. It is a good, quick read.