Tens of millions of Chinese users may have suffered personal information leakage after Yahoo’s data breach incident took place in 2013, said a Chinese Internet expert.

“All Chinese users who use Yahoo email accounts to log in to social media platforms such as Weibo may have lost their personal information due to the [hack]. Though many of the accounts are now inactive, users may still use the account to log in to other platforms,” Ge Jia, a Chinese Internet analyst, told Xinhua News Agency.

Echoing Jia, many Chinese internet security experts suggested that Chinese Yahoo users change their username and password in an effort to tackle the data breach.

Yahoo, now part of Verizon subsidiary Oath, announced on Oct. 3 that all Yahoo accounts were affected by the data breach that took place in 2013. The new announcement shows that the leakage was more severe than the disclosure in 2016, in which it said over one billion of about three billion accounts had likely been affected.

Names, email addresses, hashed passwords, phone numbers, and even security questions and answers may have been compromised, according to experts, potentially leading to severe personal information leakage.