Why can a classified computer use a CD but not a USB flash drive? Can't a CD be implanted and spread Trojan horses or viruses like a USB flash drive?

The storage mechanism of U disk is different from that of CD-ROM, and the hidden files of CD-ROM will be displayed after storage, which improves the ability to identify Trojan virus. In addition, we usually use a one-time burning CD, which is only equivalent to one-way data transmission, which greatly improves the security. Of course, this only eliminates the vast majority of Trojan viruses. But it's much safer than USB flash drive.

Finally, copying data with CD is much more troublesome than using USB flash drive, which will inevitably raise the selection threshold for copying data.