I had a little linux server years ago and after a setup forgot to change my SSH port. One day I noticed my network was slow and after poking around realized that I had someone knocking at my port trying pass after pass with like 15 - 30 sec between attempts, watched this person for 2 days laughing at the 8-10 char passwords they were using, my password was a sentence. I then shifted the port to the 30k range and all was silent on my ports, always remember to change default ports, fun times