Explanation
The greatest concern for an information security manager in this situation would be the security of the data that is being processed by the third-party service provider working from a remote site. This could be a concern because the data may not be adequately protected from unauthorized access, manipulation, or theft. A secure communications protocol should be used to ensure the confidentiality and integrity of the data in transit.
Additionally, the information security manager should ensure that the third-party service provider has appropriate security controls in place to protect the data, such as access controls, error checking, and malware protection. This information can be found in the ISACA's Certified Information Security Manager (CISM) Study Manual, Section 5.2.