The HPD you have on hand will always be secure, just like the Secure FTP.
What we need is something that you can put your HPD in to work for you and attach a risk factor to it, so that's why I came up with stock markets.
Now I guess you could use the bank of a mega-corp just like you use the stock market, and deposit HPD to gain interest, however those accounts / shares will be hackable. Bank accounts with interest are usually guaranteed investments for a bank, so it should be the same as a stock purchase but with a lower risk factor.
There will be some sort of mini game in there, where you would involve one or more of your servers to hack, acquire and track the stock / bank accounts of others. Some sort of semi-private account system will be created in order to prevent transfers of HPD between accounts, but still make it possible to steal stuff.
But, for those that want their HPD safe and sound, they can always have the HPD in the secure stash attached to each HP account