What digital evidence should be examined to understand how Thomas' account information was compromised after he clicked a phishing email?

The most pertinent digital evidence to examine in order to understand how Thomas' account information was compromised after he clicked on a phishing email is email messages. Analyzing the email messages can reveal crucial information such as the specific content of the phishing email, any malicious links or attachments it contained, and how it prompted the user to divulge sensitive information.

By reviewing the email, investigators can identify the sender's address, any indicators of spoofing, and the language used that might have been designed to deceive the recipient. Additionally, examining the email headers can provide insights into the route the email took to reach Thomas, which can assist in tracing the source of the phishing attack.

While other options like social media accounts, router logs, and flash drive contents may provide some context or additional information, they are not directly related to the initial compromise stemming from the phishing email. Social media accounts might reveal if there is further unauthorized access but won't directly explain the phishing scenario. Router logs could offer information about network traffic, but wouldn't pinpoint the specific actions taken as a result of the phishing attempt. Flash drive contents are largely irrelevant in context of a phishing scheme related to an email. Therefore, examining the email messages is the most direct method to uncover how the compromise occurred.