If you want to use antivirus only when you want,than try BitDefender Free Edition which is free and it lacks Real-time scanner. You can also use any On-Line antivirus from my webpage). But i don’t understand why do you wan’t to use such antivirus!? Whole point of On-Access (Real-Time) protection is that it blocks viruses at entry point. When you are already infected,its usually too late and you have to clean the whole mess which takes time. avast!'s On-Access module prevents your computer from even being infected in first place,so you don’t have to worry about what’s gonna happen next. As someone before said avast! has a very minimal impact on the systems performance,so i recmmend that you use at least On-Access protection with Normal Sensitivity for providers.