Most commercial software, audio and video on writeable media is write-protected when distributed.
These mechanisms are intended to prevent only accidental data loss or attacks by computer viruses.
A determined user can easily circumvent them either by covering a notch with adhesive tape or by creating one with a punch as appropriate, or sometimes by physically altering the media transport to ignore the write-protect mechanism.
In the case of computer devices, attempting to violate it will return an error to the operating system while some tape recorders physically lock the record button when a write-protected cassette is present.
Write blocking, a subset of write protection, is a technique used in computer forensics in order to maintain the integrity of data storage devices.