The port that should be disabled on the firewall is port 3389. Port 3389 is used by Remote Desktop Protocol (RDP), which is a protocol that allows remote access and control of a Windows system through a graphical user interface. RDP can pose a security risk if it is not properly configured or secured, as it can expose the system to unauthorized or malicious access from external sources. Therefore, port 3389 should be disabled on the firewall unless it is needed for legitimate purposes.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 3, Lesson 3.3, Objective 3.3

The most likely cause of the server crashing and the application being inaccessible is that the unauthorized software installed by the update is malware that corrupted the system files or compromised the security of the server. To restore access to the application while minimizing downtime, the administrator should scan and remove any malware from the server, and then reformat the server and restore the image from the latest back-up. This will ensure that the server is clean and has a working configuration of the application. Verified References: [How to Remove Malware from a Server]

A subscription license is a type of license that grants the user the right to use a product or service for a fixed period of time, usually a year. The user pays a recurring fee, regardless of how much they use the product or service. Subscription licenses are common for cloud-based software and services, such as Microsoft 3651 or DocuSign2.
References = 1: Compare All Microsoft 365 Plans (Formerly Office 365) - Microsoft Store(https://www.microsoft.com/en-us/microsoft-365/buy/compare-all-microsoft-365-products) 2: DocuSign Pricing | eSignature Plans for Personal & Business(https://ecom.docusign.com/plans-and-pricing/esignature)

A MD5 checksum is a value that is calculated from a file using a cryptographic hash function. A MD5 checksum is used to verify the integrity of a file by comparing it with the original value provided by the manufacturer or the source. If the MD5 checksums match, it means that the file is authentic and has not been corrupted or tampered with. If the MD5 checksums do not match, it means that the file is potentially corrupt or malicious and should not be installed12. A DLF configuration (A) is a setting that determines how a dynamic link library (DLL) is loaded into memory and executed by an application. A DLF configuration does not check the integrity of a file. A MBR failure (B) is a problem that occurs when the master boot record (MBR) of a disk is damaged or corrupted, preventing the system from booting. A MBR failure does not check the integrity of a file. ECC support is a feature that enables error-correcting code (ECC) memory to detect and correct data errors in RAM. ECC support does not check the integrity of a file. References: 1
https://www.comparitech.com/net-admin/file-integrity-monitoring-tools/ 2
https://csrc.nist.gov/CSRC/media/Presentations/Firmware-Integrity-Verification-Monitoring-and-Re/images-me

The backup type that only records changes to the data blocks on a virtual machine is snapshot. A snapshot is a point-in-time copy of a virtual machine (VM) that captures the state and data of the VM at a specific moment.
A snapshot can be created instantly and with minimal overhead, as it only stores the changes made to the VM after the snapshot was taken. A snapshot can be used to restore the VM to its previous state in case of data loss or corruption.