Very interesting article here. Only those banks who have physical presence and have banking licences are allowed to do banking in Second Life. Second Life said:
"As of January 22, 2008, it will be prohibited to offer interest or any direct return on an investment (whether in [Linden dollars (L$)] or other currency) from any object, such as an ATM, located in Second Life, without proof of an applicable government registration statement or financial institution charter. We're implementing this policy after reviewing Resident complaints, banking activities, and the law, and we're doing it to protect our Residents and the integrity of our economy."
All this to be taken with a grain of piquant salt!!!