Never Give Your Information To 10 Minute Old Startups
Many folks in the security community might suggest a) An oblique warning publicly like "There exists a security problem with this; I have mailed the devs" b) actually mailing the devs c) waiting for confirmation of fix or a reasonable time and only then d) tar-and-feather.  The term-of-art for this is "responsible disclosure."This incentivizes people to fix things quickly and preserves the reputational value of breaking into things without researcher-vendor relations getting adversarial when you announce something like "I harvested a couple dozen of your customers' API keys" or "Here's an exploitation roadmap you can follow in your browser" in a public forum.