How is broadband different from the network I use at work?
Corporate bonds and government networks are typically protected by many layers of security, ranging from network firewalls to encryption. Moreover, they usually have support staff who maintain the security and availability of these network connections.

Although your ISP is responsible for maintaining the services they provide to you, you probably will not have dedicated staff on hand to manage and operate your home network. You are ultimately responsible for your own computers. As a result, it is up to you to take reasonable precautions to make your computers from accidental or intentional abuse secured.