Alternatively, imagine that a bank receives an e-mail from a client, which instructs that all the client's funds should be transferred to a private numbered bank account in the Cayman Islands. Once again, without a handwritten signature, how does the bank know that the e-mail is really from the client? The e-mail could have been written by a criminal attempting to divert the money to his own Cayman Islands bank account. In order to develop trust on the Internet, it is essential that there is some form of reliable digital signature. —The Code Book,
Simon Singh

What type of evidence appears in this paragraph?

What information is important to protect, according to the example of the bank?