One of the best free firewalls available, Comodo Firewall includes a message center, that from time to time pops up invitations for an upgrade to a commercial version of the program.

This can be annoying, but it is not necessary, you can avoid it easily without any crack or hack.

Right click Comodo’s icon in the Windows system tray and select the Open option, then go to More > Preferences, and uncheck the option “Enable Comodo Message Center” (at the first, “General”, tab).

Enjoy!