My SSH servers got hacked ...
long time back
And my bare bone telnet servers were never ever hacked.
Sometimes I think isn't ssh better ??
Quite strange I know...but in real experience the less software u install...the better system behave
Just to add...1 of my servers with firewall carshed again and again due to misconfiguration or bug of some sort...and I had to reinstall with more than 12 hours of downtime.
Other servers without any firewall stuff....are sailing smoothly with 100% uptime from past 3-4 months...yeah some amount of bandwidth is lost due to codered etc attacks...but My linux machine is safe and steady as yet without any firewall.
Just to conclude...I do use ssh on all of my new servers and try to implement firewall whereever I find place or need for it...but sometimes...I just think..