What practice should be avoided when dealing with Trojan incidents?

Allowing programs to execute that are sent via instant messaging is a practice that should definitely be avoided when dealing with Trojan incidents. Trojans are a type of malicious software designed to deceive users into executing them, often masquerading as legitimate software or files. When users permit the execution of such programs, especially those received through instant messaging, they significantly increase the risk of inadvertently installing and executing malicious code.

In contrast, disconnecting from the Internet and using secure file transfer methods are both prudent steps to take in the event of a suspected Trojan infection. Disconnecting restricts the malware's ability to communicate with external servers, potentially halting the spread of the infection or preventing data exfiltration. Using secure file transfer methods can help ensure that files sent or received are verified and less likely to contain malicious content.

Running antivirus tools regularly is another best practice, as it can help in detecting and removing Trojans and other malware before they can cause significant harm. Therefore, avoiding the execution of unverified programs is crucial for preventing the infection or further complications stemming from a Trojan incident.