CompTIA A+ 220-902

Answer: B - SCR is an executable file type and thus poses the maximum security risk of the file types listed above. It holds a screensaver application.

Key Takeaway:
One should not open any unknown attachments in an email. Hackers can send any file by renaming or changing its actual extension. For example, any executable file can be sent by a different extension. SCR is an extension for a screen saver, which is an executable file. Opening unknown executable files can pose a very high security risk. Take extra caution before you open an SCR extension file.