Haven't read the spec, but yes they can. I know several common USB devices that actively prevent field upgrades of their firmware for security reasons, an exam

Haven't read the spec, but yes they can. I know several common USB devices that actively prevent field upgrades of their firmware for security reasons, an example would be the Yubikey (http://www.yubico.com/faq/upgrade-yubikey-firmware/ http://www.yubico.com/faq/upgrade-yubikey-firmware/).