Weiss Serota partner and firm IT manager Eric Hockman said in a statement to DBR that "we did experience an attempted attack on our network," but "our quick reaction appears to have stopped the attack before it went very far." He added that the firm's incident consultant advised, "that there is virtually no chance that any data exfiltrated and we have encountered no evidence that it was."

At press time, both firms declined to identify the nature of the attacks, but a source familiar with the situation at Weiss Serota said the firm was the victim of a ransomware attack that temporarily suspended internal operations.

They are the latest in a series of cyberattacks targeting law firms.

Earlier this month, Am Law 100 firm Seyfarth Shaw was the victim of a "sophisticated and aggressive malware attack that appears to be ransomware," a firm statement said. Days after Seyfarth confirmed the attack, the firm said it was still working on restoring critical systems, but said that there was no evidence client data was stolen. A firm statement Oct. 19 —seven days after the attack was announced—said the firm's critical systems "are now restored and fully operational."

Also this month, Am Law 100 immigration firm Fragomen, Del Rey, Bernsen & Loewy disclosed that an unauthorized party accessed the personal information of employees at Google, a client of the firm. Fragomen said it discovered the incident last month.

Hackers use ransomware attacks to prevent a firm from operating and servicing clients. Other attacks focus on the clients themselves. "An email attachment somebody clicks on will give the [hackers] access to the law firm's files," said Jason Kellogg, a partner at the Miami litigation boutique Levine Kellogg Lehman Schneider + Grossman who has represented law firms and their clients in recent cybersecurity cases, in an interview.

"[The hacker] will wait and put in keywords. If 'wire' or 'settlement' comes up, the hacker will start monitoring email traffic," Kellogg continued, speaking generally about cyberattacks. By intercepting client emails and changing wire information, hackers can divert funds meant for firms or clients to their own accounts.

In July, Holland & Knight was sued for its role in such a scheme. The firm had been hired to handle a stock sale valued at $3.1 million. According to the complaint, a hacker intercepted emails related to the stock sale and asked the firm to wire the money to a bank account in Hong Kong, which it did. As of July, the funds were not recovered.

Law firms carry cybersecurity insurance to cover the damage from cyberattacks, but not all cybersecurity insurance is created equal. "I've seen some policies that only cover a very narrow set of circumstances," Kellogg said. "They put caps on coverage. It's called 'cybersecurity' even though it's very basic."

Last year, Am Law 10 firm DLA Piper was reportedly in a dispute with its cybersecurity insurer, Hiscox, after the company failed to pay for a multimillion-dollar insurance claim over the ransomware attack that crippled the firm in 2017.

Michael Mora contributed to this report.