In my opinion, and experience,I would say that the quick scan misses alot. Tuhrough my experience with Avast, and alot of scanning I find that the quick, scan skims through basically if you are already assured that your computer is safe so just like a skim throgh...I have found out after doing a quick scan and finding nothing on my comp. I than do a full scan and it does find stuff right after....I also rely on the Custom Scan where I set up Avast to Scan "all start up programs, Memory and Tootkits" is probably the most accurate I can get Avast...Also I prefer a "boot scan" over "Full Scan" or "Quick Scan" because it's much Faster and Scans your Computer before anything gets a change to start and change settings on my Comp..This is just my opinion through experience with Avast through the years of use....Luck..