A、By transferring money among different accounts. B、By replacing the missing money through gambling. C、By making computer errors

In many businesses, computers have largely replaced paperwork, because they are fast, flexible, and do not make mistakes. [22]Many banks advertise that their transactions are "untouched by human hands" and therefore safe from human temptation. Obviously, computers have no reason to steal money. But the growing number of computer crimes shows they can be used to steal.
    Computer criminals don’t use guns. And even if they are caught, [23]it is hard to punish them because there are no witnesses and often no evidence. A computer cannot remember who used it: it simply does what it is told. A clerk at a New York bank used a computer to steal more than $1,500,000,000 in just four years. [24]No one noticed this theft because he moved the money from one account to another. Each time a customer he had robbed questioned the balance in his account, the clerk claimed a computer error, then replaced the missing money from someone else’s account. This clerk was caught only because he was a gambler. When the police broke up an illegal gambling operation, his name was in the records.
    Most computer criminals have been minor employees. Now police wonder if this is "the tip of the iceberg." As one official says, "[25]I have the feeling that there is more crime out there than we are catching. What we are seeing now is all so poorly done. I wonder what the real experts are doing—the ones who know how a computer works."
22. Why do many banks claim that their transactions are safe?
23. Why is it difficult to punish computer criminals?
24. How did the New York bank clerk cover up his crime?
25. What are the police officials concerned about?