At CyberGuard Corp, an industry-leading cybersecurity consulting firm, you are the Principal Incident Responder known for your expertise in dealing with high-profile cyber breaches. Your team primarily serves global corporations, diplomatic entities, and agencies with sensitive national importance.

One day. you receive an encrypted, anonymous email Indicating a potential breach at WorldBank Inc., a renowned international banking consortium, and one of your prime clients. The email contains hashed files, vaguely hinting at financial transactions of high-net-worth individuals. Initial assessments indicate this might be an advanced persistent threat (APT),likely a state-sponsored actor, given the nature and precision of the data extracted.

While preliminary indications point towards a potential zero-day exploit, your team must dive deep into forensics to ascertain the breach's origin, assess the magnitude, and promptly respond. Given the highly sophisticated nature of this attack and potential geopolitical ramifications, what advanced methodology should you prioritize to dissect this cyber intrusion meticulously?