First of all, thanks for your attention to this matter. I’ve followed all the steps you said. I canceled the Malwarebytes Anti-Malware analysis and the aswmbr analysis (they were going to last a lot). I got two different results for the MCSHIELD analysis. The first one (before FRST restored the computer) showed no malware on the stick, but the second one (done automatically by the program when the system initiated) showed and destroyed a malware in it. I attach the two results, and the FRST log file. During all the process the stick has been plugged in. Until now, the alert has not popped again.

Can I keep using the usb stick normally? Should I do anything else?

Thanks again for your help.