In other cases, the computer suddenly becomes unstable. A common problem is failure to start up or to find the hard drive. How it spreads A boot sector virus is usually spread by infected floppy disks. In the past, these were usually bootable disks, but this is no longer the case. 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.