Final answer:
A sniffer is the type of software used to view usernames and passwords over a network, which can potentially lead to cybersecurity threats if used maliciously.
Step-by-step explanation:
The type of software that can be used to view usernames and passwords broadcasted over a network is known as a sniffer. This type of software is designed to capture and analyze the traffic passing through a network. It is capable of intercepting data packets and extracting information such as usernames and passwords, especially if the data is not properly encrypted. Utilizing such software for malicious purposes is illegal and considered a form of cybercrime. It's essential to practice ethical behavior and understand the importance of cybersecurity.