It's *most definitely* a hacking attempt being waged via hacked servers.
I recommend that you block these 4 IP#'s in an .htaccess file placed in your root ftp directory (if using Apache)...
193.150.170.160
81.23.227.170
66.89.120.35
65.39.172.139
ex.
<Limit GET>
order deny,allow
deny from 193.150.170.160
deny from 81.23.227.170
deny from 66.89.120.35
deny from 65.39.172.139
allow from all
</Limit>
If any other such IP#'s show up in your logs, just add 'em in.
