removing clamav with purge leaves database I uninstalled clamav with apt-get remove --purge clamav but still I have this 100MB folder: du -shc /var/lib/clamav Why is this not deleted on purge? And how can I find out if some other installed program still uses this folder?

`clamav` on at least Debian (you don't mention what distro you're using) doesn't contain the database. For that `clamav` has a dependency on `clamav-freshclam | clamav-data` so make sure that both of those are also purged.