Can one bruteforce attack easily shut down a server?

Somebody got one of my servers pretty good, trying different username combinations and searching for files with tons of different proxies... I was down for a good ten minutes. Its happened alot before, but never shut me down...

Example:
[Wed Apr 2 02:50:15 2003] [error] [client 195.120.178.135] user Flexscan not found: /members
[Wed Apr 2 02:50:15 2003] [error] [client 217.106.203.250] user comeon1 not found: /members
[Wed Apr 2 02:50:15 2003] [error] [client 217.97.135.253] user [email protected] not found: /members
[Wed Apr 2 02:50:16 2003] [error] [client 195.120.178.135] user again not found: /members
[Wed Apr 2 02:50:16 2003] [error] [client 193.52.244.40] user bwheels not found: /members
[Wed Apr 2 02:50:16 2003] [error] [client 193.52.244.40] user bukos not found: /members
[Wed Apr 2 02:50:16 2003] [error] [client 61.74.252.10] user ArmyStud not found: /members

I increased my maxclients, that didnt help much. Not much you can do when your attacked eh? Moving everything to isprime, maybe that'll help alil...