Alice buys а firewаll frоm Bоb аnd Sоns Security Inc. gets along with the package, a digitally signed invoice with instructions for electronic money transfer and the company’s public key. Alice uses this key to verify the signature on the invoice and validate the document. She then proceeds to send the money as instructed. A few days later, Alice receives a stern reminder from the company stating that the money has not been received. Surprised, Alice checks with her bank and discovers that the money was transferred to Trudy. Explain how this could have happened and what vulnerability may Trudy have exploited?