One purpose of the md5sum is to verify that the ISO image has not been corrupted during the download process or during the burning of the image to the DVD/USB memory stick. A corrupted ISO image might just be the reason for the live session failing to load or a broken installation.
Another purpose is to verify that the ISO image is authentic. But if the same web site that is providing the ISO image is also providing the md5sum then everything comes down to whether you trust that particular web site
It is like someone phoning and pretending to be your bank. They provide a phone number so that you can verify that the caller really is from your bank but when you phone that number you do not get through to the bank but to another criminal who pretends to be the bank.
If you cannot trust the Lubuntu/Ubuntu download site then the fact that the md5sums match is no guarantee that the ISO image does not contain malicious software.
I trust the Ubuntu download site. I have never had malicious code installed on my machine either by running a Ubuntu live session or by installing Ubuntu or any of its flavours.
Regards
Did not check lubuntu .iso with md5sum. Should I be worried?
