Hello, in my Awstats statistic software, i can see:

Viewed traffic * 333 676
(2.03 visits/visitor)
(90.18 Pages/Visit)
(103.46 Hits/Visit)
102.93 MB
(155.92 KB/Visit)
Not viewed traffic * 110,739 112,280 1.48 GB

That traffic eater was one IP address which i banned by adding it into .htaccess file, line:

deny from

I see that the bandwidth was taken by robot without user agent filled:
Unknown robot (identified by empty user agent string)

Unknown robot (identified by 'robot')
Unknown robot (identified by 'spider')

Please how can i ban such a robot using .htaccess rewrite rule?