Before infection of a hard drive, DA_Boys checks for a two-byte signature of 0xBB, 0x78 in the boot record at offset 0x48. If it does not find a DOS 5.0 boot sector, it does not attempt to infect the drive. This means that multiple-boot systems are fairly safe from infection, as long as the non-DOS partition is physically first on the drive. On a system where a DOS 5.0 boot sector is located first on the drive, DA_Boys infects only the first partition on each physical hard drive.

Upon infection, DA_Boys makes the assumption that the boot sector is located at side 1, cylinder 0, sector 1. DA_Boys does not actually check the partition table for the proper location. If the boot sector is located elsewhere in the DOS partition, DA_Boys does not infect the host.

DA_Boys modifies the original boot sector without first saving a copy. The DOS boot sector contains code used only if the system files cannot be found during boot-up. As this code is infrequently used (hard drives rarely lose their operating systems), the virus overwrites this code and data and places itself in these areas. This keeps the viral code small and prevents it from having stealthing capabilities. DA_Boys does not contain any apparent harmful trigger code. Portions of the original boot sector remain intact and make references to some of the overwritten areas.