Not sure how to reply.
If you are asserting you know for a fact Swedish "covidbevis.se" have been hacked already I appreciate it. It would be interesting to learn your source though.
Or perchance you completely missed the point? The looks of the document doesn't matter. The document and its QR code could be printed on toilet paper for all anyone's going to care. My whole point why I even brought it up is that US-style easily forged documents is 19th century tech and basically a joke.
I'm certainly not saying the style of certificate discussed here is bullet-proof but as far as I can tell we instead have a QR code (in your mobile, or on that roll of toilet paper) pointing the officer to an active online government database where the person's vaccination data can be validated, so you'd have to either inject false entries into the official database or spoof an entire site and just hope the officer can't be bothered to certify he's at the right site. Which is complicated by the fact the certificate is only valid for 90 days, then you need to update your document, which (again to the best of my knowledge) means data is pulled from the national health registry, an covid certification entry is created, and you're given a document whose QR code points to it for the benefit of, not you, but the customs officer in the country you're trying to enter.