As I recall, there was a Bitcoin wallet service which relied on securing the access key behind the '#' in the URL for its security -- turns out it's not perfect

As I recall, there was a Bitcoin wallet service which relied on securing the access key behind the '#' in the URL for its security -- turns out it's not perfectly reliable and shouldn't be used for protecting money. Likewise for files you really need to be secure. Since boring crypto shouldn't have weird failure modes like this, I'm thinking this design is a big mistake? EDIT: I think it was Instawallet and apparently while they had robots.txt set to prevent crawling, the theory was people typing their URL into Google (or Omnibar) would alert Google to the URL and it got into search results anyway. I know that web-keys is based on the theory that since the fragment isn't sent by User-Agents in the Request-Uri that it's secure, but there are things that see the full URL which aren't conforming agents, and it just seems risky for any long-lived secret.