Olá,
Fiz os comandos recomendados, eis os resultados:
ClamAV update process started at Mon May 2 16:24:47 2016
WARNING: Your ClamAV installation is OUTDATED!
WARNING: Local version: 0.98.7 Recommended version: 0.99.1
DON'T PANIC! Read
http://www.clamav.net/support/faqmain.cvd is up to date (version: 57, sigs: 4218790, f-level: 60, builder: amishhammer)
daily.cld is up to date (version: 21513, sigs: 90448, f-level: 63, builder: neo)
bytecode.cvd is up to date (version: 277, sigs: 47, f-level: 63, builder: neo)
rafael@Rafael-PC:~$ freshclam
ERROR: Can't open /var/log/clamav/freshclam.log in append mode (check permissions!).
ERROR: Problem with internal logger (UpdateLogFile = /var/log/clamav/freshclam.log).
Aparentemente, no primeiro fez o que devia, apesar de não ter visto nenhuma atualização sendo baixada, porém no segundo, tentei separadamente o comando freshclam, porém o mesmo erro persiste.