Which control is most effective for detecting attacks involving unauthorized data transfers within a company's network?

Monitoring irregular peer-to-peer communication is the most effective control for detecting attacks involving unauthorized data transfers within a company's network. Peer-to-peer communication can facilitate the unauthorized sharing of sensitive data, making it crucial to identify and analyze these irregular patterns. This form of monitoring allows security teams to detect potential data exfiltration attempts, unauthorized file sharing, or other malicious activities that may not be caught by other security measures.

By focusing on the analysis of traffic and communication trends between peers on the network, organizations can pinpoint unusual behaviors that may signify malicious intent. This proactive approach enhances the ability to respond to potential threats before they escalate into more significant incidents.

The other options, such as implementing a web content filtering system or upgrading the company's firewall, focus on different aspects of security. While they play important roles in safeguarding the network, they may not specifically address unauthorized data transfers as effectively as monitoring peer-to-peer communication does. Similarly, installing unauthorized devices is not an effective control; instead, it is a risk that needs to be mitigated. Thus, the targeted nature of monitoring peer-to-peer communication makes it the best choice for detecting unauthorized data transfers.