JUNK: log entries

Server operators
1

I noticed these messages in the ntpd log I’ve never seen before:

Aug 20 16:55:02 char-ntp-pool ntpd[502]: JUNK: M1 V4 0/61616161 48/61616161 from 94.177.164.13:51469, lng=500
Aug 20 16:55:04 char-ntp-pool ntpd[502]: JUNK: M1 V4 0/61616161 48/61616161 from 94.177.164.13:51469, lng=500
Aug 20 16:55:06 char-ntp-pool ntpd[502]: JUNK: M1 V4 0/61616161 48/61616161 from 94.177.164.13:51469, lng=500

What causes those?