Why scan for viruses?

If I run antivirus and antispyware software continuously, and update both daily, why should I also run scans? If the software didn't recognize the virus and block it in the first place, why would it pick it up on a scan?

Why scan for viruses?aurora

Some viruses are not recognized as such until after they reach your system and begin to propogate. Worms will grow inside if left undetected which can ruin your system files. Running a scan prevents these from getting to big and doing too much harm. Without scanning, it is left as a non-virus, because it wasn't properly detected when you got it on your drive. Hope this helps

Why scan for viruses?download

if you're aware of your computers stability, and its safe, you would not need too, merely a wise precaution, if being used by several users, or downloading zip files or installers, or after a long extend use while scanner is off, or for any new unknowns, and a firewall would help if online even without scanners,

..
You do not have to update your virus protection every day once a week is usually when an update is made. Scanning finds hidden virus's on your computer that just updating your virus program will not find. Scan once every two weeks I know it takes a long time to do but it usually finds virus's. There are some virus's that disable your virus protection in the registry so please scan once every two weeks to protect your computer. This happened to me many years ago so this is why I know now what to do to avoid this happening again.
This would be the case for trojan viruses. These types of viruses are not always known because of their ability sometimes to change its name. Therefore the anti-virus programs would have to also search for behaviors in order to determine if a file may be a danger.