Secure Bank Ltd., a mid-sized financial institution, prides itself on offering secure digital banking services to its customers. Recently, the bank…

Secure Bank Ltd., a mid-sized financial institution, prides itself on offering secure digital banking services to its customers. Recently, the bank became a target of a sophisticated malware attack that exposed multiple vulnerabilities in its IT systems. (I) Incident 1: An employee of Secure Bank received an email from what appeared to be a reputable software vendor, offering a "free system optimization tool". Believing it to be legitimate, the employee downloaded and installed the tool. However, it was a cyber-attack, disguised to appear as harmless software. Once installed, it created a backdoor that allowed attackers to access the bank's internal network. (II) Incident 2: The attackers leveraged to target employees' smartphones. This malware was introduced through phishing SMS (smishing), which prompted employees to click on malicious links. The malware exploited outdated operating systems on the devices to extract sensitive corporate information. (III) Incident 3: The attackers executed a malware on the bank's systems by exploiting legitimate tools such as PowerShell and Windows Management Instrumentation (WMI), the attackers initiated a series of commands to explore and manipulate the bank's network. (IV) Incident 4: A critical server was encrypted by a cyber-attack, disrupting operations for three days. This encrypted all critical financial data, rendering the system inoperable. Investigations revealed that the attack originated from a phishing email sent to an employee. The email contained a link that exploited an unpatched vulnerability in the server. From the above which of the cyber-attack incident that Secure Bank Ltd. became victim of, is described as "Ransomware?"