The Vatican has decided that worshippers who want to wash away their sins will not have to go all the way to Rio de Janeiro for the World Youth Day (WYD) to do it - they can follow Pope Francis on Twitter instead.

In the past the faithful travelled from all over the world to participate in one of a limited number of events where plenary indulgences were offered. Pope Francis has granted such an indulgence - the highest form of forgiveness - to devotees who arrive in Rio de Janeiro to attend the 28th WYD.

In an unusual step, Francis has decided to extend the pardon to those streaming the Catholic festival online or watching it on TV.

A decree by the Holy See states that the faithful who are "legitimately impeded" will be able to obtain the indulgence provided they follow the festival's ceremonies "through television and radio or, always with the due devotion, through the new means of social communication".

"Get it out of your head immediately that this is something mechanical, that it is enough to click on the internet to get an indulgence," warned Monsignor Claudio Celli, president of the Pontifical Council for Social Communications.

"You don't get an indulgence as you get a coffee out of a coffee machine.

"Watching the Rio mass online, following Francis from an IPad or logging in to Pope2You.net [the Holy See's YouTube] won't be enough," Celli said.

Considered as pardoned

Only those followers who are moved by the Pope's 140-character tweets and fully understand their meaning will be considered as pardoned, he explained.

"What really matters is for the tweets the Pope will post from Brazil and the pictures he will upload on Pinterest to have a real spiritual effect on people's hearts," Celli said.

A plenary indulgence grants a full pardon from the temporal punishment for sins that have already been forgiven in confession. That translates as a shorter penance for the faithful to atone or a shorter time his/her soul will have to spend in purgatory.

The WYD, from 23-28 July, coincides with Francis' first trip overseas since his election in March. Some two millions pilgrims are expected to attend the festival.

Francis' Twitter account is in nine languages, with a total of more than seven millions followers.

Francis is characteristically modest about his tech savviness.

"Once I wanted to give him a CD player. He [Francis] asked me how many buttons it had," Julio Rimoldi, editor of Argentinian Catholic TV channel Canal 21, said. "'Three or four,' I said. 'Then it's not for me.' He replied. 'It gives me a headache if they are more than two.'"

Pope Francis WYD
Pope Francis (Reuters)