It's known as Britain's listening post, operating secretly to detect threats against national security.
But now GCHQ has emerged from the shadows of cyber space to become the first of the country's spy agencies on Twitter.
Its maiden post, sent at 11.02am from the account @GCHQ, simply said "Hello, world".
Twitter's more than a decade old and firmly embedded in the lives of hundreds of millions. But joining the site is a bit of a surprise move for the organisation - their public ventures are rare and their work is kept secret.
This step towards greater transparency comes after the service came under intense scrutiny in the wake of revelations by Edward Snowden in 2013.
A GCHQ spokesman said: "We know that some will say we're joining the Twitter party slightly late but we're the first intelligence agency in the UK to do this and it's a big step for the organisation as we become more open about the work we do to keep Britain safe."
FYI, the new account is already racking up followers.