The FBI is using BitTorrent clients, specifically modified for law enforcement purposes, to track down people who share child porn and prosecute them. The software in question is configured to download complete files from a single suspect, to confirm that this person has the illegal content in his or her possession.

To combat the distribution of child pornography on the Internet, U.S. law enforcement is using BitTorrent to track down and catch perpetrators.

File-sharing networks and tools are used to transfer all sorts of files, including pornographic footage of children.

The Department of Justice in the U.S. sees these cases as a high priority and has successfully prosecuted many cases in recent years. Several of these, were concluded with help from P2P file-sharing software.

A few years ago applications with shared folders, such as Limewire, allowed the FBI to pinpoint infringers who were actively sharing illegal content. The evidence in these cases was relatively strong and led to many convictions.

However, now that Limewire and other popular “shared folder” applications are no longer available, law enforcement has switched to BitTorrent.

While there have been similar cases before, this week we first spotted an indictment where BitTorrent was used to find someone sharing these files. In the affidavit, signed by a Homeland Security Investigations agent, the process is explained in detail.

The agent describes BitTorrent as a “very popular” file-sharing network that users typically connect to, through torrents they download from search engines such as Isohunt or The Pirate Bay.

These torrent sites don’t store any material themselves, the affidavit clarifies, but the perpetrators and law enforcement can use these sites to find illegal content.

“Law enforcement can search the BitTorrent network in order to locate individuals sharing previously identified child exploitation material in the same way a user searches this network,” the affidavit reads.

“By searching the network for these known torrents, law enforcement can quickly identify targets in the searcher’s jurisdiction.”

The FBI and other law enforcement agencies use these search engines to find torrents that are known to link to child porn. They then load the torrent files in modified torrent clients and obtain IP-addresses and other information from the associated trackers.

The software in question is modified to download complete files from a single source, so the investigator knows that the person on the other end has a full copy.

“There is law enforcement-specific BitTorrent network software which allows for single-source downloads from a computer at a single IP address, meaning that an entire file or files are downloaded only from a computer at a single IP address as opposed to obtaining the file from multiple peers/clients on the BitTorrent network.

“This procedure allows for the detection and investigation of those computers involved in sharing digital files of known or suspected child pornography on the BitTorrent network,” the affidavit adds.

In the present case a search by FBI special agent David Hand led to a Simi Valley man, who was arrested and indicted by a federal grand jury last week.

In addition to distributing child pornography, a follow-up investigation unveiled more gruesome details. The indictment alleges that the man also took 83 images and three videos of a 6-year-old girl with his iPhone.

Based on the above, the man faces lengthy prison terms for producing, distributing and possession of child pornography.