The question is who still has Java installed? I removed it long ago due to security issues. I also just checked my Win 10 file associations for .jar. The extension doesn't exist. I believe it only does so when Java is installed.
Also for clarification, you cannot run executable code directly from a .jar file as for example, can be done from a .hta file. You have to create the executable code outside of JAVA RTE and run it from the .jar file as done below: http://stackoverflow.com/questions/11339979/how-to-execute-script-from-jar-file The Microsoft article shows the execution of .vbs script malware. If you're on Win 10 and using an AV product that uses the AMSI interface which Windows Defender also uses, the script would be intercepted and scanned for malware signature prior to execution. -EDIT- So what we are talking about here is pattern matching machine learning; something AV vendors like Eset have been doing for years.