प्रोग्राम कोड का एक टुकड़ा, जो अपनी प्रतियां बनाकर फैलता है, उसे ________ कहा जाता है।

Assertion (A): The execution phase of a computer virus is the stage where the virus becomes active and performs its intended malicious actions such as data corruption or file deletion. Reason (R): The propagation phase is when the virus executes its payload and destroys data in the host system.

Which country created the world's first computer virus for MS-DOS, known as 'Brain'?