These restrictions apply to applets that are downloaded over the public Internet or company intranet. They do not apply to applets on the client’s local disk and in a directory that is on the client’s CLASSPATH. Local applets are loaded by the file system loader and, as well as being able to read and write files, are allowed to exit the virtual machine and are not passed through the bytecode verifier. The JDK (Java Development Kit) Appletviewer also slightly relaxes these restrictions, by letting the user define an explicit list of files that can be accessed by downloaded applets. In a similar way, Microsoft’s Internet Explorer 4.0 introduced the concept of ‘zones’, and some zones may be trusted and others untrusted. Java applets loaded from certain zones are able to read and write to files on the client’s hard drive. The zones with which this is possible are customizable by the Network Administrators.