http://www.zabbix.com/documentation/1.8/manual/config/items :

File checksum, calculated by algorithm used by UNIX cksum.

older zabbix agents, vfs.file.cksum[/etc/services] :
3198325890

1. cksum /etc/services
   3198325890 764360 /etc/services

latest trunk agent, vfs.file.cksum[/etc/services] :

1. zabbix_get -s localhost -k vfs.file.cksum[/etc/services]
   270945646

1. ls -l /etc/services
   rw-rr- 1 root root 764360 2010-07-05 14:34 /etc/services

likely a regression, caused by ZBX-3794