Final answer:
Countermeasures is the OPSEC process step that focuses on measures to prevent the exploitation of vulnerabilities.
Step-by-step explanation:
The OPSEC process step that focuses on measures that effectively negate an adversary's ability to exploit vulnerabilities is called Countermeasures.
Countermeasures involve implementing safeguards and protective measures to prevent the exploitation of weaknesses by adversaries.
Examples of countermeasures include applying software patches and updates to fix vulnerabilities, using firewalls to block unauthorized access, and implementing strong encryption to protect sensitive data.