Boot & Program Viruses - Types and Habitats
Boot and program
viruses were the first viruses. They are generally made of executable code
that hides inside device boot programs and application
programs, and are usually targeted for a specific computer operating system.
These were the earliest types of computer viruses, and remained
relatively common in
the wild until overtaken in 1998 by script and
Boot viruses. Boot
viruses hide in the boot code for a media device, such as a disk or
CD, and run automatically when the media is loaded since boot programs
are always the first code loaded from any device. Boot viruses proliferated
on floppy disks and even CD's into the late 1990's, but aren't seen as
often these days with the decline in importance of transferable, bootable
The first computer
boot virus was built by a 15 year old kid named Rich
Skrenta in 1982 for
Apple II computers. Called “Elk
it would activate whenever a floppy disk was booted on a computer, install
itself on the computer, and then infect other disks used later. Once every
50 times an infected floppy was inserted in a computer it would display the
Elk Cloner: The program with a personality
It will get on all your disks
It will infiltrate your chips
Yes it's Cloner!
It will stick to you like glue
It will modify ram too
Send in the Cloner!
the virus into the wild in early 1982 by infecting his school’s computer
and giving out disks at a computer club. Since viruses were not yet known
and there were no safegaurds, it spread around the country
and continued to pop up on Apple II computers for years afterwards.
The first boot
virus to infect Microsoft computers was called Brain, created in 1986 by
two Pakistani brothers, and displayed the phone number of their
computer repair business.
Program viruses. Program
viruses can travel on media like a CD or across the Internet by
email attachment. They hide in an apparently useful program and then run
when the program is opened. They are often called trojan
horse viruses, after the hollow wooden horse containing soldiers that
Ulysses and the Greeks gave to Minerva during the Trojan war, and from
which the soldiers emerged that night to open the gates of the city of
Troy to the Greek armies, thereby causing the city's downfall.
Program viruses may be deliberately hidden in a program by the developer,
or surreptitiously attached after the fact at some point along its travels
from computer to computer. Program viruses are also sometimes the vector
of infection for boot viruses and worms.
Virus infection. A greeting card program emailed to you from a friend
might display a holiday animation and song, while at the same time installing
a remote access virus program that gives a distant hacker control over your
computer whenever you're connected to the Internet. Similarly, a shareware
program downloaded and emailed to you by another friend might have been infected
with a virus on his computer or the server where it was stored.
The first thing a boot or program virus often does is insert commands and
settings in the operating system so that they can operate freely, undetected,
and unaudited, without warning messages or access log records. Some of
them even change the Basic Input Output System (BIOS) that interfaces between
the computer's hardware and software to help mask their activities.
The most sophisticated program viruses include "stealth viruses", which
encrypt their contents to try and avoid detection by virus
protection software, and "polymorphic viruses", which alter their
content every time they replicate to try and avoid detection, which exhibits
behavior just like real viruses. Most anti-virus
programs can still catch most of these types of viruses.