A puzzling circumstance.
A difficulty that has to be resolved or dealt with.
A set of moves required to complete a climb.
A question to be answered, schoolwork exercise.
Objection.
Difficulty in accepting or understanding or refusal to accept or understand.
Causing a problem; problematic; troublesome.
Difficult to train or guide; unruly.
A disease caused by such an infectious agent; a viral illness.
Any malicious or dangerous entity that spreads from one place or person to another.
A quantity of such infectious agents
Any type of malware.
A type of malware which can covertly transmit itself between computers via networks (especially the Internet) or removable storage such as disks, often causing damage to systems and data; also computer virus.
A submicroscopic, non-cellular structure consisting of a core of DNA or RNA surrounded by a protein coat, that requires a living host cell to replicate, and often causes disease in the host organism; such agents are often classed as nonliving infectious particles and less often as microorganisms.
To send or infect an electronic device with a computer virus.