A.I. is helping attackers in other ways. Some have used chatbots to draft phishing emails and ransom notes, cybersecurity experts said. Others have used A.I. to parse large quantities of stolen data and determine what information might be valuable. Without help from A.I., attackers could sometimes break into computer networks within minutes, Mr. deSouza said, but with the help of A.I., breaches can take just seconds.

Some hackers specialize in breaking into systems and then selling off their access to other attackers. Those handoffs used to take as much as eight hours, as hackers negotiated the sales and passed along the compromised entry points, Mr. deSouza said. Now that process has accelerated to about 20 seconds, he said, with hackers sometimes using A.I. agents to speed up the process.