Unknown robot (identified by empty user agent string) - eating bandwidth

[Fli]

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



Viewed traffic *
333

676
(2.03 visits/visitor)
60,962
(90.18 Pages/Visit)
69,942
(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 1.2.3.4

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?