A full scan performs a comprehensive and thorough check of your whole system. It usually checks your system memory, startup programs, system backup, email databases, hard drives, and any removable storage drives. A quick scan only checks a few areas including startup programs, system memory, and boot sectors. It may not detect all malware, but it can usually give you an idea if your computer has a virus. As to when you should do either, we recommend a full scan once per week, during computer usage downtime (such as late at night). A quick scan can be done anytime you like, but it's usually only necessary if you notice suspicious activity on your PC.