I bought a new computer yesterday which contained a new anti-virus program.
It nagged me several times to register and pay for the software. After seeing this message a few times, I decided to remove the software and stop being nagged.
The software did remove itself — only to be replaced with another nagware message saying "Your computer is at risk of viruses. Click here to protect yourself."
I believe this tactic is called "damned if you do, damned if you don’t!"