  In an analysis of the US, the UK, and the German stock market we find a
change in the behavior based on the stock's beta values. Before 2006 risky
trades were concentrated on stocks in the IT and technology sector. Afterwards
risky trading takes place for stocks from the financial sector. We show that an
agent-based model can reproduce these changes. We further show that the initial
impulse for the transition might stem from the increase of high frequency
trading at that time.
