_kerberos error in logs

[cyberale]

Hello,

I have found a lot of entries in the messages log file like that:

Jul 31 22:13:22 server named[1725]: client 127.0.0.1#34881: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#44152: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#35656: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#37698: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#51306: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#39399: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#44544: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#37948: query (cache) '_kerberos.net/TXT/IN' denied
Jul 31 22:13:22 server named[1725]: client 127.0.0.1#43417: query (cache) '_kerberos.net/TXT/IN' denied

There are about of 1000 of them. There are entries like this everyday, but not as much as this time...

They seem to appear always after some denied query cache entries:

Jul 31 21:46:42 server named[1725]: client 186.47.101.200#34523: query (cache) '115.0.0.10.in-addr.arpa/PTR/IN' denied
Jul 31 21:53:09 server clamd[9294]: SelfCheck: Database status OK.
Jul 31 22:03:09 server clamd[9294]: SelfCheck: Database status OK.
Jul 31 22:10:23 server named[1725]: client 186.47.101.200#36338: query (cache) '116.0.0.10.in-addr.arpa/PTR/IN' denied
Jul 31 22:13:09 server clamd[9294]: SelfCheck: Database status OK.

Any idea what's going on ?