How to keep port scannings away?

[Charles Luo]

hi, guys   A few days ago, I installed snort-1.3.6 on one of my company LAN machines. By checking log files daily, I found that our firewalls are scanned 3-4 times daily, . Some of them scan normal ports, such as 80, 8080, 111; but some of them scan ports like 1243, 21, 22, 1080 etc . I suppose that the people scan the later ones could have some tendencies in mind.   So, can anyone suggest me how to keep those scannings away ? If it is unavoidable, what I should do in order to reduce the damage as lower as possible?   Thank you in advance, Charles