Can I block viruses from a USB stick by scanning it before opening its folder?
Referring to my answer to this question (before it was migrated):
No, scanning the drive without "opening the folder" isn't a secure way to protect against viruses on the drive. It's very risky to insert what you believe to be a compromised USB device into your PC, no matter what AV you have installed.
If you desperately need files from the drive (to quote myself):
you should attempt to only insert the drive into a secondary PC running some live version of a linux distro, preferably one you wouldn't mind completely wiping afterwards.
If not, just cut your losses and physically destroy the pendrive. USB viruses are extremely efficient these days, and are more frequently able to persist in hardware between wipes (either on small partitions on the pendrive, or by loading themselves into the firmware of the infected machines hardware).
The point is, there is no guaranteed way to insert that drive without risking further contamination.
It depends. In older times there was an autostart facility when inserting a data DVD/CD-ROM or USB stick but on modern systems this is usually no longer active by default. It might still be possible to corrupt the file system on a stick in a way which causes code execution when the system tries to access the device, and there are USB sticks with a writable controller which could have been modified to be a Bad USB device.
While antivirus works in lots of cases it is not a foolproof thing and there are methods to bypass it. If you must assume that your USB device is infected I would not recommend it to put into into your system any longer, no matter if you have antivirus or not.
Depends on what it has on it. There are some attacks and malware which affects the signals that the device sends to the computer - most famously the BadUSB attacks, which let flash drives claim to be input devices - in which case merely plugging a device in could allow it to do things ranging from the annoying (hitting enter at random) to the malicious (loading web pages containing drive by malware).
Safest thing is to replace the USB drive, but you could try examining it using a liveboot environment, although bear in mind that even that could result in problems if you miss anything, or if the live CD mounts your actual system drives.