The most recent had bought a laptop from the High street and got straight down to using the laptop. McAfee was still there waiting for you to buy and activate. There is no reason now not to have basic Antivirus protection for free with the likes of AVG, Microsoft and others. I have always installed an antivirus product on all pc and laptop builds so the owner does not have to. It is easy to remove and add your own at a later stage.
Microsoft Security Essentials is easy to install and recently has found things that the well-known paid antivirus software products failed to find.
So install security software, keep up to date and allow scanning the system also apply windows updates when prompted.