A floppy disk does not need to be bootable to transmit the virus. Any disk can cause infection if it is in the drive when the computer boots up. The virus can also be spread across networks from file downloads and from e-mail file attachments. In most cases, all write-enabled floppies used on an infected PC will themselves pick up the boot sector virus. This is no longer the case.
Viruses are now more dangerous and spread much more easily.
Some CMOS setups can be configured to prevent writing to the boot sector of the hard drive. This may be of some use against boot sector viruses. However, if you need to reinstall or upgrade the operating system, you will have to change the setting back to make the MBR writable again. Most antivirus packages contain routines that can perform both tasks. A good virus protection software package is Norton AntiVirus .