In its latest attempt to keep up with the times the Vatican has married one of its oldest traditions to the world of social media by offering "indulgences" to followers of Pope Francis' tweets.

The church's granted indulgences reduce the time Catholics believe they will have to spend in purgatory after they have confessed and been absolved of their sins.

The remissions got a bad name in the Middle Ages because unscrupulous churchmen sold them for large sums of money. But now indulgences are being applied to the 21st century.

But a senior Vatican official warned web-surfing Catholics that indulgences still required a dose of old-fashioned faith, and that paradise was not just a few mouse clicks away.

"You can't obtain indulgences like getting a coffee from a vending machine," Archbishop Claudio Maria Celli, head of the pontifical council for social communication, told the Italian daily Corriere della Sera.

Indulgences these days are granted to those who carry out certain tasks – such as climbing the Sacred Steps, in Rome (reportedly brought from Pontius Pilate's house after Jesus scaled them before his crucifixion), a feat that earns believers seven years off purgatory.

But attendance at events such as the Catholic World Youth Day, in Rio de Janeiro, a week-long event starting on 22 July, can also win an indulgence.

Mindful of the faithful who cannot afford to fly to Brazil, the Vatican's sacred apostolic penitentiary, a court which handles the forgiveness of sins, has also extended the privilege to those following the "rites and pious exercises" of the event on television, radio and through social media.

"That includes following Twitter," said a source at the penitentiary, referring to Pope Francis' Twitter account, which has gathered seven million followers. "But you must be following the events live. It is not as if you can get an indulgence by chatting on the internet."

In its decree, the penitentiary said that getting an indulgence would hinge on the beneficiary having previously confessed and being "truly penitent and contrite".

Praying while following events in Rio online would need to be carried out with "requisite devotion", it suggested.

Apart from the papal Twitter account, the Vatican has launched an online news portal supported by an app, a Facebook page, and it plans to use the online social networking site Pinterest.

"What really counts is that the tweets the Pope sends from Brazil or the photos of the Catholic World Youth Day that go up on Pinterest produce authentic spiritual fruit in the hearts of everyone," said Celli.