Since its first public release in 1996, the Java platform had not been open source, although the Java source code portion of the Java runtime was included in Java Development Kits (JDKs), on a purportedly "confidential" basis, despite it being freely downloadable by the general public in most countries. Sun later expanded this "confidential" source code access to include the full source code of the Java Runtime Environment via a separate program which was open to members of the public, and later made the source of the Java compiler "javac" available also. Sun also made the JDK source code available confidentially to the Blackdown Java project, which was a collection of volunteers who ported early versions of the JDK to Linux, or improved on Sun's Linux ports of the JDK. However, none of this was open source, because modification and redistribution without Sun's permission were forbidden in all cases. Sun stated at the time that they were concerned about preventing forking of the Java platform.