Here is a manual to install Clamav or Avast antivirus on Ubuntu 9.10
Open a Terminal Window (Applications->Accessories->Terminal) and type the following:
sudo apt-get install clamav clamtk
Access it through Applications->Applications->System Tools->Virus Scanner .
Open a Terminal Window (Applications->Accessories->Terminal) and type the following:
wget http://files.avast.com/files/linux/avast4workstation_1.3.0-2_i386.deb && sudo dpkg -i avast4workstation_1.3.0-2_i386.deb
Access it through Applications->Accessories->avast! Antivirus .