The Dublin Rape Crisis centre website has been hacked by a group claiming to be Islamic State militants.

The centre received a number of calls on Sunday morning after a black banner with white writing appeared on the site’s homepage with the message: ‘Hacked by Islamic State (ISIS), We Are Everywhere’.

The banner also contained a logo in Arabic, which translated as “There is no God, but God” and a Facebook url which linked to a profile under the name Mohammed Ali. The Facebook page has since been removed.

On Monday the chief executive of the Dublin Rape Crisis Centre, Ellen O’Malley-Dunlop, described the hacking as “sinister”, particularly given the vulnerability of many users on the site.

“We were absolutely shocked by it,” said Ms O’Malley-Dunlop, who highlighted the “poignancy” of the hacking taking place on International Women’s Day.

“If it was a hoax, whatever the situation, it’s sinister.

Hi all just to say drcc website wasn't hacked specifically it was a wordpress hack. Thankfully we've now been able to remove the banner! — Dublin Rape Crisis (@DublinRCC) March 9, 2015

“Our site would be used by people in very vulnerable situations and often, people who would use website to get help, some may be suicidal. Callers would be very traumatised after being victim of rape or assault.”

Ms O’Malley-Dunlop said the centre was notified of the banner at 11.30am on Sunday by a user on the website. She contacted gardaí who said they are now investigating the matter. She also contacted the site manager.

The banner was removed from the site on Monday morning after contact was made with staff from Wordpress.

“The site itself wasn’t hacked, it’s secure,” said Ms O’Malley-Dunlop. “It was just the banner on the homepage.”

“We’ve spoken to Wordpress and updated our system. They’ve updated our version of wordpress and changed all our passwords. They’re on top of it.”

The Dublin Rape Crisis centre tweeted on Monday morning the website was secure, reassuring followers that only the site’s homepage had been affected by the hack.

Meanwhile, there were a number of similar hacking reports around the world over the weekend, all pertaining to sites using a Wordpress server.

The Sequoia Park Zoo in California, the MERS Goodwill charity in St Louis and the Moerlein Lager House in Cincinnati, all wordpress users, were hacked with the same black and white banner over the weekend.

A natural history museum in Hvolsvollur in Iceland was also reportedly hacked with the banner.

The Lost Coast Outpost website reported that before being taken down, the Mohammad Ali Facebook page posted a list of sites around the world believed to be hacked by the same group, with websites in Germany, Italy, the UK and Sweden.

The Rape Crisis Centre’s national 24-hour hotline is: 1800 778888