Risk on DCS/SIS System Internal S/w exchange with 3rd party Vendors(PASS/TALES)

In view of Cyber security Support many Chemicals/Oil & Gas Industrial Giants are availing the services from companies like TALES/PAS for vulnerability management..
Neverthless these vendors will get access to the Production control systems software..
How Process industries shall be able to effectively prevent sensitive data leaks to competitors by any malicious acts of the cyber security services companies.