Scanning USB drives for malware

Hi people.

Recently my brother downloaded some nasty software with even nastier bundled crap (yeah, I know, it's always the "brother", I know, clichè :wink:).

Windows Defender stopped some trojans and a subsequent scan found 4 of them.
I also manually removed some crap from the windows uninstaller app (some creepy chinese stuff) and made further scans with Defender and Malwarebytes. Also checked with Hijack This.

So far, it appears all clean, boot included.


However I had a USB stick and a hard drive connected while this happened and I would like to be reasonably sure that there's no crap on it.
I have sensible stuff and various software backup on it and I cannot simply format them.

The drives work fine and have no odd behaviour or files, however my suspicion was raised by the fact that on both of them there were hidden files put on "show" setting. It was nothing harmful, just USB drive software but since I could not remember if it was I that had set hidden files on "Show", it raised my suspicions. It could have been me while going on "crap hunt" before, but cannot really remember.

Could you suggest me a malware scanner (preferably free) specifically made to sanitize usb drives?