How do you imply something that doesn't have a visible effect?

Question

How do you imply something that doesn't have a visible effect? For example, it's easy to imply someone died by saying something like:

A pool of blood formed under her feet.

But how do you imply that someone installed a virus? Without mentioning that the virus was installed? Is there a way to do this? I can say something like:

Robots started making strange noises.

But this is so terrible I am thinking there must be some better way, and people would probably have some insights on this.

Answer 1

What is infected?

Everything has computers in it nowadays. There could be any number of effects depending on what is infected, what the virus is supposed to do, and what the desired literary effect is. Are you instilling fear? Is it comic effect? Is there a specific (criminal) purpose?

• Your phone starts spamming advertising at you.
• If it makes a funny noise, DESCRIBE the funny noise. A high-pitched whine above the normal operations. Stuttering. Constant cycling of some functions like motors, or cooling systems, etc.
• A robot spontaneously shuts down and reboots.
• The thermostat goes out of control, displaying a cold temp when it's sweltering.
• Your computer tells you you're wrong and to stop ("Dave. What are you doing, Dave? I can't let you do that.")
• An unknown icon appears on the control display. It seems to run and run, but doesn't do anything. You get the blue screen of death, then it resets and starts up again.
• Voice software switching languages spontaneously, or repeating syllables randomly. The voice switches from female to male.
• The background resets to defaults.
• The device brings up a prompt saying it's infected with a virus. Then one of the above happens, and it quits telling you it's infected.

I doubt any of these things apply to your specific case. So ask yourself, "What is the device, what does it do, what would happen if it malfunctioned, and (most importantly) how does the malfunction advance my story or entertain my reader?"

Answer 2

You have to compare it to something. Establish what normal behavior looks like earlier in the story, then have it change.

An on the nose example: Have a person comment something like: "wow, look how smooth that robot's movements are". Then later, when the robot starts jerking, you know something is off.