If you tell a secret to the wind, don't be mad it told the trees...

Praise be to Allaah.  

Secrets are a kind of trust, and thus they are a kind of contract or covenant which must be kept. It is necessary to be harsh with those who disclose them, because they are betraying a trust and breaking their promise; and those who deserve to a ta’zeer punishment should be punished.  

“Verily, Allaah commands that you should render back the trusts to those, to whom they are due”

[al-Nisa’ 4:58] 

So if keeping secrets is obligatory, then disclosing them is haraam. The Prophet (peace and blessings of Allaah be upon him) told a secret to ‘Aa’ishah and Hafsah and entrusted them with it, but they disclosed the secret, and Allaah rebuked them for that. 

Disclosing secrets is one of the signs of hypocrisy, because it comes under the heading of betraying a trust. 

It was narrated from ‘Abd-Allaah ibn ‘Amr that the Prophet (peace and blessings of Allaah be upon him) said: “There are four qualities, whoever has all of them is a pure hypocrite, and whoever has some of them has a characteristic of hypocrisy until he gives it up: when he is entrusted with something he betrays that trust; when he speaks he lies; when he makes a promise he breaks it, and when he disputes he resorts to lies and falsehood.” Narrated by al-Bukhaari, 34; Muslim, 58. 

Fatwa on keeping secrets...