If you burn a disk, it stays put. The disk will never be changed. Every time you use that burnt DVD, you get the same results, unless it gets scratched. On the

If you burn a disk, it stays put. The disk will never be changed. Every time you use that burnt DVD, you get the same results, unless it gets scratched. On the other hand, let's say you have a USB stick. 1. Download installer package. 2. Create bootable USB stick. ... maybe leave the stick plugged in, and surf the internet. 3. You boot, successfully install a clean system, then: ...leave the stick plugged in, and surf the internet. or ...leave the stick unattended, and in the physical presence of an enemy. 4. Fall victim to malware which goes undetected: ...specially crafted malware corrupts the USB stick, and includes a malicious payload as part of the *NEXT* install. or ...someone builds an evil corrupted debian package and slips it into the installer, so that it piggybacks into the *NEXT* install. 5. Now, you have a corrupted installer spreading its hazards to every installation thereafter. You have no idea whether the installer's integrity has been compromised, because the USB stick remains writable. With a DVD ISO, there is only one chance to attack, and it's during the download. This is easily mitigated if Valve tells us the exact size in bytes and what SHA-256 hash of the downloaded file is (over an SSL connection), so that we can verify the integrity of the download by matching hashes. If that matches, and we burn the disk, we know the disk remains secure and tamper resistant (more so than a USB stick), so long as it is not damaged or scratched or anything.