The term for a program that replicates itself to spread to other computers is a computer virus. A virus attaches itself to legitimate programs or files and can disrupt operations or cause harm to the infected system. When a user runs the infected program, the virus activates and may replicate itself, spreading to other systems. Countermeasures include antivirus software that detects, quarantines, and removes these malicious programs, emphasizing the importance of digital security practices.