Filler Virus

Virus Name: Filler Aliases: V Status: Rare Discovered: 1991 Symptoms: BSC; Master Boot Sector Altered; decrease in available free memory Origin: Hungary Eff Length: N/A Type Code: BRhX - Resident Boot Sector & Master Boot Sector Infector Detection Method: ViruScan, Sweep, F-Prot, AVTK, IBMAV, NAV, NAVDX, VAlert, ChAV Removal Instructions: M-Disk/P or DOS SYS for system diskettes General Comments: The Filler virus was submitted in January, 1992. It was originally reported in the public domain in Hungary in 1991. Filler is a memory resident infector of diskette boot sectors and the hard disk master boot sector (partition table). Filler is a stealth virus, when it is memory resident, anti-viral programs will not be able to detect its infection of the hard disk master boot sector, and will have difficulty detecting its presence on diskette boot sectors. When the system is booted from a Filler infected diskette, the Filler virus will install itself memory resident at the top of system memory but below the 640K DOS boundary. Total system memory will not decrease, but available free memory as indicated by the DOS CHKDSK program will have decreased by 8,192 bytes. The system hard disk's master boot sector will be infected at this time, if it was not previously infected with Filler. Once the Filler virus is memory resident, it will infect non-write protected diskettes exposed to the system. The infection of the diskette usually occurs when the boot sector is accessed for some reason. The Filler virus will write a copy of itself to the last track of the diskette which is not normally accessable by DOS. It will also store the original boot sector on this track. The virus then alters the boot sector to point to the viral code. The Filler virus is a stealth virus. When it is memory resident, scanning infected diskettes will not detect the presence of the Filler virus when using scanning technology. CRC-type checking programs may be able to determine that the boot sector has been altered. In the case of the hard disk master boot sector, if Filler is memory resident, neither CRC-type checking or scanning programs will be able to determine the Filler virus's presence. If you suspect you have a Filler virus infection, power down your system and then reboot from a known uninfected, write protected system diskette, and then check the system with anti-viral software. It is unknown what Filler might do besides replicate.