I use firewall rule: and this rule blocks these ports almost of every my client. I am affraid of not to block any service needed by my clients. What are that ports needed for? Is better to block them or allow them. Or block almost every client means that almost everybody is infected by messenger worm?

Usually used for NetBIOS stuff , it is better to block them .

Yes, if they want to do this windows networking stuff over the Internet, it should be done with an encrypted VPN. If you see those ports, you can safely block it.

Thanks for your help.