This document describes a secure collaborative processing architecture for detecting Man-in-the-Browser (MitB) attacks. The architecture consists of Edge Gateways deployed at each financial institution and private clouds that form the collaborative processing system. Edge Gateways anonymize sensitive data using Shamir's secret sharing scheme and send anonymous data to the collaborative processing system. The system aggregates information through MapReduce-based computations. If suspicious cyber threat activities are detected, the anonymous data resulting from computation are revealed to the financial institutions. The paper shows how this architecture can be used to detect MitB attacks while preserving privacy of sensitive data during collaborative event processing.