Security

What is the risk of having port # 21, 139,135,1025,445 open? My freind connected to airport wireless and sent me the mentioned port numbers and told me if I have those ports somebody can get acces cause problem + this is what he said tom me “A few of the ports are extremely serious they cause DOS (Denial of Service) attacks which will bring a network to it’s knees”

What do you guys think?

Thank you,