The primary purpose of requiring source code escrow in a contractual agreement is to ensure the source code is available. Source code escrow is a service that involves depositing the source code of a software or system with a third-party agent or escrow provider, who can release it to a designated beneficiary under specific conditions, such as bankruptcy, termination, or breach of contract by the software vendor or developer.
Source code escrow can help to protect the interests and rights of the software user or licensee, who may need access to the source code for maintenance, modification, enhancement, or troubleshooting purposes. The IS auditor should verify that the contractual agreement specifies the terms and conditions for source code escrow, such as the escrow agent, the escrow fees, the deposit frequency and format, the release events and procedures, and the verification and audit requirements. References: CISA Review Manual (Digital Version)
1, Chapter 3, Section 3.2.2

Digital watermarks are hidden marks or codes that can be embedded into digital files, such as images, videos, audio, or documents. They can be used to identify the source, owner, or authorized user of the data, as well as to track any unauthorized copying or distribution of the data. Digital watermarks can help prevent data leakage by deterring potential leakers from sharing sensitive data or by providing evidence of data leakage if it occurs.
The other options are not as effective as digital watermarks in preventing data leakage. Ensuring that paper documents are disposed securely can reduce the risk of physical data leakage, but it does not address the digital data leakage that is more prevalent in today's environment. Implementing an intrusion detection system (IDS) can help detect and respond to cyberattacks that may cause data leakage, but it does not prevent data leakage from insiders or authorized users who have legitimate access to the data. Verifying that application logs capture any changes made can help audit and investigate data leakage incidents, but it does not prevent them from happening in the first place.
References:
* What is Data Leakage?
* What is Digital Watermarking?

A disaster recovery plan (DRP) is a set of procedures and resources that enable an organization to restore its critical operations, data, and applications in the event of a disaster1. A DRP should be aligned with the organization's business continuity plan (BCP), which defines the strategies and objectives for maintaining business functions during and after a disaster1.
To ensure that a DRP is effective, it should be tested regularly and thoroughly to identify and resolve any issues or gaps that might hinder its execution2345. Testing a DRP can help evaluate its feasibility, validity, reliability, and compatibility with the organization's environment and needs4. Testing can also help prepare the staff, stakeholders, and vendors involved in the DRP for their roles and responsibilities during a disaster3.
There are different methods and levels of testing a DRP, depending on the scope, complexity, and objectives of the test4. Some of the common testing methods are:
* Walkthrough testing: This is a step-by-step review of the DRP by the disaster recovery team and relevant stakeholders. It aims to verify the completeness and accuracy of the plan, as well as to clarify any doubts or questions among the participants45.
* Simulation testing: This is a mock exercise of the DRP in a simulated disaster scenario. It aims to assess the readiness and effectiveness of the plan, as well as to identify any challenges or weaknesses that might arise during a real disaster45.
* Checklist testing: This is a verification of the availability and functionality of the resources and equipment required for the DRP. It aims to ensure that the backup systems, data, and documentation are accessible and up-to-date45.
* Full interruption testing: This is the most realistic and rigorous method of testing a DRP. It involves shutting down the primary site and activating the backup site for a certain period of time. It aims to measure the actual impact and performance of the DRP under real conditions45.
* Parallel testing: This is a less disruptive method of testing a DRP. It involves running the backup site in parallel with the primary site without affecting the normal operations. It aims to compare and validate the results and outputs of both sites45.
Among these methods, full interruption testing would best demonstrate that an effective DRP is in place, as it provides the most accurate and comprehensive evaluation of the plan's capabilities and limitations4. Full interruption testing can reveal any hidden or unforeseen issues or risks that might affect the recovery process, such as data loss, system failure, compatibility problems, or human errors4. Full interruption testing can also verify that the backup site can support the critical operations and services of the organization without compromising its quality or security4.
However, full interruption testing also has some drawbacks, such as being costly, time-consuming, risky, and disruptive to the normal operations4. Therefore, it should be planned carefully and conducted periodically with proper coordination and communication among all parties involved4.
The other options are not as effective as full interruption testing in demonstrating that an effective DRP is in place. Frequent testing of backups is only one aspect of checklist testing, which does not cover other components or scenarios of the DRP4. Annual walk-through testing is only a theoretical review of the DRP, which does not test its practical implementation or outcomes4. Periodic risk assessment is only a preparatory step for developing or updating the DRP, which does not test its functionality or performance4.
References: 2: Best Practices For Disaster Recovery Testing | Snyk 3: Disaster Recovery Plan (DR) Testing
- Methods and Must-haves - US Signal 4: Disaster Recovery Testing: What You Need to Know - Enterprise Storage Forum 5: Disaster Recovery Testing Best Practices - MSP360 1: How to Test a Disaster Recovery Plan - Abacus