If you publish an article for anyone to read that details how to attack the website, damn skippy you're responsible. 2 weeks? Around the friggin holidays? Did it ever occur to you it might take the owner longer than that to either a. contact the original website developer or b. find someone else to come in and fix it?
Yes, it is probably illegal in some jurisdictions in the sense you can be sued. Criminally? Without knowing a specific jurisdiction, can't say.

