Dublin Rape Crisis Centre
The hacked website of the Dublin Rape Crisis CentreDublin Rape Crisis Centre

The FBI is investigating cyber attacks over the weekend on several western websites allegedly by someone with links to Islamist terror group Isis.

The websites that were hacked include that of the Dublin Rape Crisis Centre in Ireland, the Southwest Montana Community Federal Credit Union, Third Street Brewhouse, and the Montauk Manor.

The hacked websites carried a picture of the black Isis flag and the words "hacked by ISIS, we are everywhere."

Southwest Montana Community Federal Credit Union and Montauk Manor have removed the Isis banner, while Third Street Brewhouse's website "is currently undergoing scheduled maintenance," and will take more than two days to come online.

No accounts at the credit union have been compromised in the attack.

Isis, or the Islamic State of Iraq and Syria, is said to have hacked hundreds of websites in the US and Europe on 6 and 7 March.

"The FBI is aware of the reported incidents and is contacting the impacted parties," the agency said.

Nevertheless, local officials and security experts said they do not have enough evidence to link the attacks to the terrorist group, noting the claim to be a hoax.

"I don't think ISIS agents would be interested in a hack like this," Silver Bow County sheriff Ed Lester in Montana was quoted as saying by a number of news outlets.

"I think this is more likely a domestic hacker rather than international cyberterrorism."

"It appears many business web sites around the country were hacked with some sort of virus through internet-based website hosting services. So the Manor itself does not appear to have been specifically targeted, and there does not appear to be any indication of regional or local targeting in this instance," said Michael Sarlo, Police chief of East Hampton Town, where the Montauk Manor is located.