Virus

Steve says:

A virus is a self-replicating program that spreads by inserting copies of itself into other executable code or documents. A computer virus behaves in a way similar to a biological virus, which spreads by inserting itself into living cells. Extending the analogy, the insertion of a virus into the program is termed as an "infection", and the infected file (or executable code that is not part of a file) is called a "host".

Doris says:

They can be really nasty so make sure you’ve had your jabs. If the symptons persist speak to Mother.