Episode 1 – Security Investigation Series – Torrents

Preface: I would like to share a methodology I used to track down an individual who was involved in downloading illegal/copyrighted movies resulting in a legal lawsuit for the company. In this post, I would try to simplify the entire thought process into simpler steps so that the reader can get an understanding on how Security Investigation can be done. Several organizations block torrent use in the Network, but several organizations don’t have such a policy in place. This investigation methodology is for people who are part of organizations of the second type 🙂

The Tip: Every Security investigation starts with a tip. In this particular case, there were three tips to work off

1. Public IP Address Registered to the Company
2. File Name of the Torrent Download
3. Time Stamps of the Download

More and More Information – Logs

Based on this above information it will be very difficult to identify who was the exact person who downloaded the Torrent. In order to do this Security Investigation, we would need logs from several devices in the IT Infrastructure. The places from where we would collect these logs can range from Network Devices to Hosts. It really depends on the level of logging enabled in the enterprise. If there are no logs, identifying this type of incident would be impossible. More and More information will help in the investigation process.

What and How much Logs to Collect is a section where I talk about typical devices in IT Infrastructure and common ways to collect, filter, analyze and store logs. For this particular investigation, the following logs were of great use:

1. Firewall Logs
2. IDS/IPS Logs
3. Authentication Server Logs
4. VPN Logs
5. DHCP Logs (if any)

Apart from the logs, we would need Corporate Network Awareness, Good Investigation skills and Patience.


1. Based on the Public IP (given in Tip 1), we can determine the Firewall from which the Traffic has been detected. This is critical in the case of Global enterprise wide Networks because, there are several firewalls deployed World over with several different Public IP addresses. Zeroing on a specific Firewall will help reduce the amount of logs to look for.

2. The next thing is to look for the above Identified Firewall logs during the Time Stamps of the event(given in Tip 3) to narrow it down to a manageable subset (this would still be Gigs of logs in case of high volume firewalls).

3. Now is the time to filter the Firewall Logs for P2P Traffic pattern. If an IDS/IPS is available in the Network and is connected to the said firewall, it makes the job easier to filter on all P2P Activity based on P2P Detect Signatures. If no IDS/IPS is available then we will have to follow a manual and time-consuming analysis for P2P.
P2P Analysis can be done in two ways. One is to look for Filter for UDP connections and see Torrent Client Port Activity. The other way is to look for Network Devices logs for Application Protocol detection capability to identify P2P activity (Symantec has a Detailed Article on Traffic Analysis of P2P here). Once the analysis for P2P is done, we can narrow down on the P2P Client set. This set is the list of Client machines that were involved in doing P2P activity during the said Timeframe (1 hour before and after the timestamp in Tip 3. This is done in order to ensure that we capture as much P2P traffic events as possible to be able to determine the exact client involved in this activity. Also, in highly utilized Network or in High Log volume environment, latency is an issue therefore having a buffer time frame is always a good option).

4. Once we have the subset of logs from the above Step, its time to identify the list of Source IP Addresses that are P2P Clients. This is present in both the IDS/IPS logs as well as Firewall Log. Doing a Union of these two data sources to narrow down the list of IP Addresses should be easy.

5. With the IP Addresses in hand, it is time to identify the hostname these IP addresses were assigned to during the specified time frame. DHCP Logs (In case of dynamic environments) can give this information. In DHCP Logs, we would get Hostname, IP and MAC Address of all the machines that have been allocated an IP within the said time frame. In case of Static IP Addresses, we would already have the information about the Hostname based on the IP addresses assigned.

6. At this juncture, we have the List of IP Addresses, the Associated Hostnames and MAC Addresses of the suspected clients. Based on the Authentication Server Logs, we can identify the Usernames associated with the above information set. Authentication Server Logs in this case are Windows (AD Logs). By filtering on the Logon events for the IP/Hostname we can identify the users.

Note: In case of VPN Connections, the VPN Connection entry has the user name information as well because VPN has a backend Authentication Component to it.

7. Once the Users are identified, we need to proceed with the Forensic Analysis of the individual machines, either remotely or physically. The clue to identifying the exact Person who did this, would be to search for the specific Torrent Filename’s (given in Tip 2) presence in the Torrent Application directory (Chances are they are not deleted by the user) or in the entire file system. The Movie file may also be present if we are lucky. In case of Movie sharing between users, its highly likely you would see Torrent + Data on one machine and Data on all other machines.

8. Once the person is identified, the appropriate teams should be notified as per the Security Investigation procedures defined for the Organization.

Note: The entire Log Collection and Analysis can be done quite easily if a SIEM Tool is available in the Enterprise. Else, it will be a painstaking job involving few hours of Analyst Time.

A Security Investigation is possible only when we have data in the right format. Right tools as well as Right mindset is also important in the Investigation process. As mentioned earlier in the post, there is no right or wrong way in Security Investigation, only a way that works best for the Current Situation and Current IT Infrastructure Setup. I would greatly welcome suggestions and additions to this post so that I can make this series more and more useful.

2 thoughts on “Episode 1 – Security Investigation Series – Torrents”

  1. Good Article. I agree that if you IDS/IPS ob is much easier in case since most of the P2P now a days on http/https.

    Alternatively you can use Proxy server logs which let you know “who”, What and When!!!
    DLP can also be used to see Prohibited contents as per security/compliance policy on data at rest or in Motion. If those logs are integrated would be nice.

    1. Good point on the Proxy logs. Actually, it will be interesting to look at P2P from a Proxy point of view. Proxies generally throw a lot of logs and identifying these specific type of traffic would be interesting. If Proxies categorize them natively, then its straight forward or else, we would need to do some traffic analysis to detect P2P in Proxy logs.
      Thanks Somesh for the valuable feedback.

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