Investigators told local paper Helsingin Sanomat that the suspects wrongly believed that the use of an insecure wireless network in commission of the crime would mask their tracks. This failed when police identified the MAC address of the machine used to pull off the theft from a router and linked it to a GE Money laptop. Police say that stolen funds have been recovered. Four men have been arrested over the alleged theft with charges expected to follow within the next two months

One of the suspects was their data security chief. Talk about a lack of ethics... Apparently none of these people were particularly good at information security either. They used a GE Money laptop, and neglected to do anything aside from using an open wireless network to mask their source. The authorities were able to identify them based on the MAC address of the laptop. None of them were keen enough to change the address, as Acidus pointed out.

Finnish security exec arrested over bank hack | The Register