Virii
If you are using Microsoft Windows, then you need anti-virus software. If you are connected to the internet and do not have current anti-virus software, then you are an irresponsible netizen.
Like vandalism and graffiti, virii do harm to society, whilst doing nothing for their authors. Despite this lack of reward, many individuals continue to create virus programs. Unlike their real-world namesakes, each virus is deliberately created in order to do harm.