Open a shell, ie terminator, and assuming you're running debian or one of that filthy whores' many offspring, try the command apt-cache search antivirus.
You'll get something like this:
zombie@apocalypse:~$ apt-cache search antivirus
amavisd-new - Interface between MTA and virus scanner/content filters
libc-icap-mod-clamav - C-ICAP Antivirus Service for c-icap (libclamav)
libc-icap-mod-urlcheck - C-ICAP URL Check Service for c-icap
clamav - anti-virus utility for Unix - command-line interface
clamav-base - anti-virus utility for Unix - base package
clamav-daemon - anti-virus utility for Unix - scanner daemon
clamav-dbg - debug symbols for ClamAV
clamav-docs - anti-virus utility for Unix - documentation
clamav-freshclam - anti-virus utility for Unix - virus database update utility
clamav-milter - anti-virus utility for Unix - sendmail integration
clamav-testfiles - anti-virus utility for Unix - test files
libclamav-dev - anti-virus utility for Unix - development files
libclamav6 - anti-virus utility for Unix - library
claws-mail-clamd-plugin - ClamAV socket-based plugin for Claws Mail
linkchecker - check websites and HTML documents for broken links
python-pyclamd - Python interface to the ClamAV daemon
python-clamav - Python bindings to ClamAV - transitional package
python-pyclamav - Python bindings to ClamAV
libclamunrar6 - anti-virus utility for Unix - unrar support
Then, just switch user to root, and:
apt-get install clamav --yes
Not that you need antivirus.