Open the Control Panel, then select Security (under "Connectivity"), then the "Auto Block" tab and check "Enable auto block".

Kiddies will scan, this blocks their IP numbers after N (by default 5) failed attempts to connect to a number of services, including SSH. My synology has blocked large parts of the internet over the past few months. :)

(only my SSH port is open to the outside so that my laptops can synchronize with my Synology via unison over SSH when I'm on the road.)