What is the most likely cause of a computer sending an email address and number to an external IP address?

The scenario describes a situation where a computer is sending an email address and number to an external IP address, which typically indicates some form of unauthorized transmission of information. The most plausible explanation within the available choices is the installation of a potentially unwanted program.

Potentially unwanted programs (PUPs) often come bundled with legitimate software and can have different functions, including adware, spyware, or malware. These programs can capture and transmit user information, like email addresses, to external servers without the user's consent. This aligns closely with the behavior described in the question where specific user data is being sent to an external IP address, as PUPs typically operate in the background, often resulting in unexpected data transmissions.

While other options reference different types of malicious activity, they do not directly fit the specific scenario of sending an email address and number. Brute force attacks usually involve credential guessing attempts without data exfiltration, while hackers exfiltrating sensitive data tend to target more significant data sets rather than just an email and number. Ransomware typically focuses on restricting access to data and demands a ransom, which may involve communication with a command-and-control server but doesn't usually involve simply sending contact information.

Therefore, the installation of a potentially unwanted program is