install kit modified

I use to create my usb stick install kit with:
Code:# dd if=downloads/ubuntu-20.04.1-desktop-amd64.iso of=/dev/sddand it worked for me.

I also use to verify the install kit before and after install with:
Code:# cmp downloads/ubuntu-20.04.1-desktop-amd64.iso /dev/sddand this also worked for me until now. It exits with end of file error, because the kit is shorter than /dev/sdd.

Now, however, for the first time, there is a difference after install at byte 480, line 4.

The kit has been created on a compromised system.

However, I have doubts that it has been modified by malicious code.

So I ran:
Code:# mount /dev/sdd1 mnt
# mount -o loop ubuntu-20.04.1-desktop-amd64.iso mnt1
# find mnt/ -exec bash -c 'file={}; cmp $file ${file/mnt/mnt1}' \; | grep differand found no difference, only that cmp does not compare directories.

Code:# lsblk -fm /dev/sdd
NAME FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT SIZE OWNER GROUP MODE
sdd iso966 Ubuntu 20.04.1 LTS amd64
2020-07-31-16-51-12-00 7,2G root disk brw-rw----
sdd1
iso966 Ubuntu 20.04.1 LTS amd64
2020-07-31-16-51-12-00 2,6G root disk brw-rw----
sdd2
vfat C26E-047E 3,9M root disk brw-rw----
sdd3
ext4 writable
a83a9b1c-36cb-4312-9aba-0359f74c0374 4,7G root disk brw-rw----What could be the cause?
Should I worry about this?