Which of the following file types is typically blocked as an email attachment due to potential virus risks?

The file type that is typically blocked as an email attachment due to potential virus risks is the executable file format, commonly represented by the .exe extension. Executable files are programs that can be run on a computer, which makes them capable of executing malicious code. Because of this capability, email systems often implement strict security measures to prevent these files from being sent or received, as they pose a significant threat to users by potentially spreading malware or viruses if opened.

In contrast, the other file types mentioned—image files (.jpg), document files (.pdf), and text files (.txt)—are generally less risky as they are not directly executable. While it's still possible for these file types to contain harmful content (such as a PDF that contains a malicious script), their structure makes it less likely for them to cause immediate harm compared to executable files. This is why executable files like .exe are subject to stricter regulations and often end up being blocked as attachments in email communications.