Issuing authentication tokens is the most reliable method of preventing unauthorized logon, as it provides a strong form of authentication that requires users to present something they have (the token) and something they know (the personal identification number or PIN) to access the system. Authentication tokens are physical devices that generate a one-time password or code that changes periodically and is synchronized with the authentication server. This makes it difficult for attackers to steal or guess the credentials of legitimate users. Reinforcing current security policies, limiting after-hours usage and installing an automatic password generator are not as reliable as issuing authentication tokens, as they do not provide a strong form of authentication and may still be vulnerable to unauthorized logon attempts. References:
* : [Authentication Token Definition]
* : Authentication | ISACA

The first thing that should be done when an intrusion into an organization network is detected is to identify nodes that have been compromised. Identifying nodes that have been compromised is a critical step in responding to an intrusion, as it helps determine the scope, impact, and source of the attack, and enables the implementation of appropriate containment and recovery measures. The other options are not the first things that should be done when an intrusion into an organization network is detected, as they may be premature or ineffective without identifying nodes that have been compromised. Blocking all compromised network nodes is a containment measure that can help isolate and prevent the spread of the attack, but it may not be possible or feasible without identifying nodes that have been compromised. Contacting law enforcement is a reporting measure that can help seek external assistance and comply with legal obligations, but it may not be necessary or appropriate without identifying nodes that have been compromised. Notifying senior management is a communication measure that can help inform and escalate the incident, but it may not be urgent or accurate without identifying nodes that have been compromised. References: CISA Review Manual (Digital Version), Chapter 4, Section 4.2.2

Source code synchronization is the process of ensuring that the source code and the object code (the compiled version of the source code) are consistent and up-to-date1. When program changes are implemented, the source code should be recompiled to generate a new object code that reflects the changes. However, if the source code is not recompiled, there is a risk that the object code may be outdated or incorrect. A compensating control is a measure that reduces the risk of an existing control weakness or deficiency2. A compensating control for source code synchronization is to compare the date stamping of the source and object code. Date stamping is a method of recording the date and time when a file is created or modified3. By comparing the date stamping of the source and object code, one can verify if they are synchronized or not. If the date stamping of the source code is newer than the object code, it means that the source code has been changed but not recompiled. If the date stamping of the object code is newer than the source code, it means that the object code has been compiled from a different source code. If the date stamping of both files are identical, it means that they are synchronized.

Sending a copy of the transaction logs to offsite storage on a daily basis would minimize the risk of losing transactions as a result of a disaster. This is because offsite storage provides a backup of the data that can be recovered in case of a catastrophic event that destroys or damages the onsite data. Storing a copy of the transaction logs onsite in a fireproof vault (B) would not protect the data from other types of disasters, such as floods, earthquakes, or theft. Encrypting or signing (D) a copy of the transaction logs and storing them on a local server would not prevent the loss of data if the server is affected by the disaster. Encryption and digital signatures are security measures that protect the confidentiality and integrity of the data, but not the availability.
Reference: CISA - Certified Information Systems Auditor Study Guide1, Chapter 5: Protection of Information Assets, Section 5.2: Backup and Recovery Concepts, Page 353.