What control best ensures that a service provider's employees adhere to security policies?

The answer focuses on a critical aspect of ensuring that a service provider's employees adhere to security policies: the inclusion of legal agreements, such as an indemnity clause, in the contract with the service provider. An indemnity clause is designed to protect the enterprise from financial loss or legal repercussions arising from breaches of security or non-compliance by the service provider’s employees. This contractual obligation creates a legal incentive for the service provider to enforce security policies rigorously among its team, as failure to comply could result in legal ramifications and costs.

In contrast, while requiring sign-off on security policies, implementing mandatory security awareness training, or modifying security policies for compliance may also contribute to adherence, these measures alone may not provide the same level of accountability or enforceability as a well-defined indemnity clause. Signing policies is useful but does not inherently ensure compliance. Training is essential for understanding security policies but may not guarantee behavior change if not coupled with enforceable consequences. Finally, adapting policies for third-party users is important, but without contractual obligations, it lacks the necessary enforcement mechanism that an indemnity clause provides. Therefore, the inclusion of an indemnity clause is pivotal in establishing a strong compliance framework between the enterprise and the service provider.