Gerald, the Systems Administrator for Hyped Enterprises, has just discovered that his network has been breached by an outside attacker. After performing routine maintenance on his servers, he discovers numerous remote tools were installed that no one claims to have knowledge of in his department. Gerald logs onto the management console for his IDS and discovers an unknown IP address that scanned his network constantly for a week and was able to access his network through a high-level port that was not closed. Gerald traces the IP address he found in the IDS log to a proxy server in Brazil. Gerald calls the company that owns the proxy server and after searching through their logs, they trace the source to another proxy server in Switzerland. Gerald calls the company in Switzerland that owns the proxy server and after scanning through the logs again, they trace the source back to a proxy server in China. What proxy tool has Gerald's attacker used to cover their tracks?