This patch makes clamav to use libunrar3. The rar3 archive support as result.
1. Install unrar3 3.4.3 with 'unrar-3.4.3_fix.patch' patch applied
2. Apply 'clamav-libunrar3.patch' patch to clamav
3. Extract files from 'clamav-libunrar3-src.tar.bz' in the clamav root source tree.

Tested with 0.86.2
Originaly from here: http://mcmcc.bat.ru/clam_rar3.html (Clamav 0.80)