My site gets exceptionally many hits from a certain range of ip address. Mostly it is just the main page.
This is last week (the number reps the amount of hits)
81.251.164.132 1689 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.165.14 999 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.166.201 263 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.167.46 65 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.168.251 59 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.170.36 908 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.172.253 365 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.173.9 88 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.174.243 688 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.189.194 19 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.189.204 1165 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.190.31 21 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.190.71 1655 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.37.185 680 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.37.211 707 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.39.198 18 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.39.36 16 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.39.51 18 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.41.201 1580 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.42.160 100 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.42.3 593 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.45.166 52 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.57.21 88 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.57.30 1275 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
81.251.63.20 1169 Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0)
What can it be?
This appears to be a bot, you can see the first IP listed on the Spamhaus PBL here: