Read the passage and choose the best answer (A, B, C or D)

With increasing development and use of computer technology, there is a new disease to worry about. Computer ‘viruses’, programs designed to sabotage computers, are infecting computers in corporations, homes and universities. These viruses spread exponentially, much like biological contagion, and then disrupt the affected systems. The virus secretly attaches itself to other programs and can then delete or alter files. The damage is generally activated by using the computer’s clock. Then, any program that is executed may be exposed to the virus, including programs spread through telephone connections. Because of the increasing incidents of virus infiltration, businesses and agencies are becoming wary of sharing software. Security policies need to be increased as immunity programs are being developed.