There's a good chance you're using a blockchain(1) to visit this website: the SSL certificate that protects your connection is published in a Certificate Transparency blockchain. If you're using Chrome, your browser verified a proof that the certificate was in fact in one of the CT blockchains. Being a blockchain, auditors (like the sysadmins at hacker news) can be sure they have the complete set of all certificates, and thus be sure they can detect any forgeries.

1) A blockchain is simply a chain of blocks. The key thing they do is allow auditing mechanisms to be sure they have the complete set of data contained in them. They're really a very simple and useful idea, which unfortunately has been hyped up by a bunch of scammers and semi-scammers. The consensus mechanisms used to secure blockchains are the interesting part, not the blockchains themselves. Although for many applications - Certificate Transparency being one of them - boring old trusted third parties seem to be good enough.

That said, if you have a stronger decentralized chain available too, you can always publish commitments to the state of your centralized chain in the decentralized chain, improving security at relatively little cost. I wrote up a particularly scalable version of that idea here: https://petertodd.org/2017/scalable-single-use-seal-asset-tr...