An improper return value is passed back from the clamav_stats_get_hostid() function in ClamAV 0.98.3. This only affects OSX systems. The following patch fixes the issue (patch is also attached):

diff --git a/libclamav/stats.c b/libclamav/stats.c
index bf7687a..4510170 100644
--- a/libclamav/stats.c
+++ b/libclamav/stats.c
@@ -595,6 +595,8 @@ char *clamav_stats_get_hostid(void *cbdata)
 
         return buf;
     }
+
+    return strdup(STATS_ANON_UUID);
 #else
     buf = internal_get_host_id();
     if (!(buf))