Viruses are made for a variety of reasons. Some viruses have been created by disgruntled employees that want revenge on a company's product. Others are created to destructively celebrate certain holidays and raise the voice of certain religious and governmental fanatics. Sadly, those that create viruses for the challenge are misdirected individuals making poor use of their skills. These scripts often result in undesired instructions and effects.
Good programmers do a thorough check of their work prior to releasing it to the public.
The WDEF virus infects the invisible desktop file of a disk. Once the disk is inserted into the disk drive the desktop file is booted into memory resulting in an infection to the hard drive desktop file. Our school recently received some donated IBM computers. The stoned virus is a boot sector virus, similar to the WDEF on the Macintosh side. Because we had been putting disks in and out of the infected machine and other machines we had several computers infected.