Although this May sound horrible, it's quite legally correct. I run a banking group in London, and this is what the regulations call for. When someone is not actively using his personal or real property, it can be subject to adverse possession, where 3rd parties can simply legally take possession of the property after being in possession for quite a length of tim.
You can Google the doctrine of adverse possession yourselves for more information. Banks probably have some kind of adverse possession type clause for their inactive, dormant accounts.
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Oh I will definitely read more on the subject. At least in my country (terminology differs but I think it is legally the same) what you are describing takes 25 years to take effect. 25 years is not 3.
I have read on Swiss banks actively using founds deposited by holocaust victims during WWII, so banks do that too.