Anonymous has been accused of boosting their numbers after an anti-Islamic list of online profiles included accounts still active and not associated with the terrorist group.
The list, placed on web app Pastebin, displayed over 20,000 social media accounts as part of their "total war" against ISIS in the wake of the Paris attacks.
In a BBC report, several accounts were found to have not been disabled like the group has claimed. There were also accounts listed which have no affiliation to terrorist groups, including Barack Obama’s official account, BBC News, Hillary Clinton, the White House, the US State Department, and the New York Times.
Anonymous had originally published the list on November 20 saying: "More than 20,000 Twitter accounts belonging to ISIS were taken down by Anonymous."
The group has since then urged its followers to report back to them if they find an account that has not been pulled down yet. "IF the accounts are back up REPORT them."
BBC Newsbeat has also found that some users saw their accounts targeted simply because their tweets were in Arabic.
Twitter user @TorReaper, a member of hacking collective GhostSec and member of various Anonymous operations, said in a video: "It is important to note that OpParis, whilst flavour of the month is not the war, it’s a battle.
"OpISIS encompasses everything and is the main fight on IS."
In a statement, the organisation said: "Hello, citizens of the world. We are Anonymous. It is time to realise that social media is a solid platform for ISIS’s communication as well as neutering their ideas of terror amongst youth.
"But at the same time, social media has proved it is an advanced weapon. We must all work together and use social media to eliminate the accounts used by terrorists."
The group also threatened ISIS, saying that it will hunt them and take down their sites, accounts, emails and expose them.
"From now on, there is no safe place for you online. You will be treated like a virus and we are the cure."
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