In 2011 the Port of Antwerp introduced an electronic release system (ERS), intended to replace the existing system for the authorization of cargo release, through delivery orders or release notes. The system was not mandatory, but was embraced by a number of carriers using the port. These carriers would send computer-generated pin codes via email to cargo receivers or their agents, as well as the port terminal. It was subsequently found that containers had been removed by a sophisticated criminal gang, who were using the containers for the illicit carriage of drugs.