Weird thing happened the other day. Called my banks automated 800 number to check on my checking account balance. Should have been around $800. Told me it was 0. Called right back thinking maybe a pushed a wrong button. $0. This time I checked to make sure it was mine, the transactions of the past were right , but still $0. Since I did this at about 1 in the morning, there was no one to talk to. Tried an hour later and my account was back to normal. At first I thought it was probably some computer maintinence glitch. Then I wondered if a clever programmer could could be emptying accounts for brief periods of time, putting them into a dummy account, which with a constant flow of money, in and out, could have a balance in the millions, which would earn interest. The bank would never know because the accounts could still balance. The customers are never going to notice they lost an hour or two of interest a month. And if the accounts are emptied in the middle of the night, few people would notice and those who did, like me, would see the problem corrected before they could find some one to complain too. Kind of like the plot in Superman III.
With interest rates so near zero, there wouldn’t be much return for the effort and risk.
True, but 1% on $10 million is still $100,000 a year. And the risk may not be that great. A lawyer wrote an article years ago about the Superman III movie and said Pryor could not be charged with a felony. Pryor didn’t steal thousands of dollars from the company, he stole fractions of a penny from millions of employees. Each employee would have to file a petty theft charge of less than one cent for each pay period. With this banking thing, the thief is not stealing from the bank, he’s stealing very small amounts from millions of people. Millions of misdemeanors.
I don’t know of any US bank that computes interest on an hourly basis.
Every bank that I know of computes interest based on the day’s closing balance (after all deposits and withdrawals have been netted against each other). So a person depositing $1 billion and withdrawing it the same day would still get $0. There are a few banks that do “continuous compounding” but they still do it on the assumption that your closing daily balance was constant throughout the day. (Continuous compounding is rarely used since the Truth In Savings Act forced banks to advertise APY rather than interest rate.)
And I doubt that an account that was receiving thousands of deposits a day with thousands of corresponding withdrawals would go unnoticed.
But plenty of unauthorized computer access felonies.
I’m wondering how hard it would be for the bank to discover all these unauthorized transactions. You’d think they would notice ten million extra every day, day in and day out. That’s 10,000 branches averaging 10,000 transactions per day.
ETA: Checked, Wells Fargo has the most at 6,300 US branches {Cite} … so each branch would have to have 16,000 extra transactions.
Another question: is it possible to hide a transaction from the account holder in your typical bank system?
Because, I mean, sure, maybe lots of bank customers would look a strange pair of transactions taking away a lot of their money and then putting it back that day, just sigh, and say “Well at least they fixed their mistake.”
But surely some people would complain, or post on social media about it… 
And from the OP, it sounds to me as if that phone access system might be, stupidly, set up to report a $0 balance based on a failure to properly access the account info.
I worked for several years in programming for a large banking system.
Every transaction to a DDA (Demand Deposit Account, like your checking or savings) was recorded & listed on the monthly statement. This was done within the DDA system itself; a transaction was only effective if it was in the system to be reported. Other systems, like for example, the one running the ATM’s, could generate a withdrawal transaction, but that was only effective if it reached the DDA system and was applied to a customers account – and if it was in the DDA system, it would be reported.
It is still done that way in my bank accounts. I know because I once had a teller make an error in entering the amount of a deposit; I noticed that in the parking lot and went back in to have it fixed. The teller did so by withdrawing the original deposit and entering a new deposit for the correct amount. And very carefully telling me that all 3 of these transactions would show up on my statement.
So this system wouldn’t work – thousands of customers would see withdrawals at strange times, like 11:59 pm, and then the same amount re-deposited at 6am. Enough of them would complain to bring this to light.
There is the penny shaving or salami slicing trick, where a fraction of a cent of interest from many accounts is deposited to the scammer’s account instead of the account that accrued the interest. But that’s a different thing because the money stays in the scammer’s account permanently, and the amount is so small that the original account holder would not notice it. I agree that it doesn’t seem possible to do what the OP suggests without it leaving obvious footprints that would very quickly be noticed.
–Mark
OP either experienced a glitch or else recently deposited $800 and should read up on the difference between current balance and available balance.
Or, yes - maintenance glitch. Servers are down for maintenance, phone lookup system asks server for balance. Server does not respond. Clever/lazy programmer has set machine to respond “zero” rather than “server unavailable for maintenance”.
I hear about someone who figured out when on Sunday night the bank did server updates/reboots. Apparently, at that time, rather than decline, the ATM would allow a daily max withdrawal. this worked fine for a while until the bank varied their maintenance window and ate his card for being overdrawn.
I do my banking with Key Bank and have discovered a daily transaction processing window which yields some potentially confusing results. During the day, you’ll can see pending transactions showing up in your balance - sometimes just minutes after making a charge or deposit - but if you check your balance on their website during the processing window, today’s activity is temporarily not shown and the balance shown is yesterday’s balance. (In their defense: a message tells you they’re doing daily processing.)
I don’t know what they do with phone banking, or if this is at all related to the OP’s issue, but it is possible for a bank to temporarily have information unavailable while they do system maintenance.