Log4J explained

A small piece of open source software written in Java called log4j was in the news around the world for the wrong reasons. It caused one of the worst affected computer vulnerabilities of recent years.
Log4j is a piece of free, open source software used by thousands of websites and business applications around the globe. The affected applications and services include big names like Apple iCloud, Microsoft Minecraft, IBM, Oracle and many others. The impact was catastrophic since the use of log4j is ubiquitous in the Java world.