Trojan blackdoor

What is trojan backdoor ?
Backdoor.Trojan is a detection name used
by Symantec to identify malicious software
programs that share the primary
functionality of enabling a remote attacker
to have access to or send commands to a
compromised computer.
As the name suggests, these threats are
used to provide a covert channel through
which a remote attacker can access and
control a computer. The Trojans vary in
sophistication, ranging from those that
only allow for limited functions to be
performed
to those that allow almost any action to be
carried out, thus allowing the remote
attacker to almost completely take over
control of a computer.
A computer with a sophisticated back door
program installed may also be referred to
as a "zombie" or a "bot". A network of
such bots may often be referred to as a
"botnet". Botnets have been well publicized
in the news over the years, with different
instances being given specific names such
as Kraken, Mariposa, or Kneber, along with
claims of hundreds of thousands of nodes
belonging to certain networks.