This document summarizes a research project that proposes a precise termination condition for the probabilistic packet marking (PPM) algorithm. The PPM algorithm allows routers to encode path information onto packets during a denial of service (DoS) attack, enabling the victim to reconstruct the attack graph. However, the existing PPM algorithm lacks a well-defined termination condition, and cannot handle multiple attackers. The proposed project aims to define a termination condition to ensure the reconstructed graph accurately represents the actual attack paths. It also extends the algorithm to support tracing packets from multiple attackers.