Microsoft issued a public warning on December 14 that hackers linked to the governments of China, Iran, North Korea, and Turkey are working to exploit a flaw in the Java-based Log4j software that could affect hundreds of millions of computer systems, including those used by governments and major corporations. According to Microsoft, the Iranian group has deployed ransomware in the past. A senior US Cybersecurity and Infrastructure Security Agency official said that there was no evidence federal networks had been breached.