Legacy BIOS boot sector check: "Extremely unlikely" meets Tetris clone ;)

[fth0]

The VirtualBox legacy BIOS uses a sophisticated method to identify invalid boot sectors, commented as follows:

    // NB: It is somewhat common for failed OS installs to have the
    // 0x55AA signature and a valid partition table but zeros in the
    // rest of the boot sector. We do a quick check by comparing the first
    // and third word of boot sector; if identical, the boot sector is
    // extremely unlikely to be valid.

There's a Tetris clone called (​TetrOS). If you use the ready-made ​tetros.img as a virtual floppy boot disk image in a VirtualBox VM you'll hit the "extremely unlikely" case.

PS: This issue also exists in the VirtualBox 7.0.x versions.