Excerpt from the linked article:
In a new study accepted for publication in the Journal of Finance, Henk Berkman at the University of Auckland, Paul Koch at the University of Kansas and Joakim Westerholm at the University of Sydney have uncovered a novel way to spot insider trading.
The researchers tracked half a million stock market accounts over a 15-year period between 1995 and 2010. The accounts were in Finland on the Nasdaq OMX Helsinki Exchange. Why Finland? It offered researchers unusual access to information about trades and information about investors, including their age.
Here in the US, there have been cases of the SEC discovering upper management of public companies trading on inside info via a relative's account. So, this is not really earth-shaking.
What I found curious is how researchers got access to private account info in Finland. Is that really public info that anyone can get access to? I do not think that is the case elsewhere, at least in the US.