Security Portal: Linux Viruses: Overview

Viruses are, by definition, malicious pieces of code that
replicate themselves.
They can do this through a variety of
methods, including “infecting” other executable files or spreading
macros and other forms of executable content (e.g. JPEGs). Viruses
are most commonly spread by users sharing files, which is
especially easy with email, and with such a wide variety of content
being available on Web and FTP servers.”

“Most viruses do not really gain the author anything – they
simply damage data and computer systems. Very few do anything, like
stealing passwords or implementing backdoors (although this is
changing, especially with distributed denial of service tools
becoming very popular). Currently, the most common viruses are
mostly macro viruses for Microsoft Office products like Word,
Excel, and Access, for a number of reasons….”

“The best defenses against Linux viruses are as follows:

Do not run software or other executable content from untrusted
sources. This includes Java and JavaScript in Web pages and
documents, rpm’s and dpkg’s from unknown sites, and compiling and
installing untrusted source code….”