The ease with which Arrahmah.com tapped into the $160bn online ad market raises questions about whether advertisers and their intermediaries are properly scrutinising the websites with which they do business. These days the placement of online ads is highly automated and they often pass through a complex chain with little human oversight.
This is not the first time that brands running ad campaigns across tens of thousands of different websites have found them appearing on undesirable sites. The UK police have in recent years cracked down on ad-supported sites that allow users to illegally download pirated films and music.
"This site violates our terms so we've taken action to terminate the account and reimburse affected advertisers."
The company did not disclose the amount of the reimbursement.
Arrahmah.com — whose slogan is "filter your mind, get the truth" — also illustrates the increasing sophistication of Islamist propaganda organisations and the expanding range of funding sources they have been able to tap. Large technology groups including Google, Twitter and Facebook have come in for criticism by security services in recent years for not doing enough to keep extremists off their platforms.
The website, which promotes extremist views in sections such as "Jihad Zone", attracts about 600,000 visits a month, according to SimilarWeb, an internet data provider. Arrahmah.com discloses prominently that Mr Abdul Rahman is its chief executive.
"He is the most important online terrorist in Southeast Asia," said Rohan Gunaratna, head of the International Centre for Political Violence and Terrorism Research at Nanyang Technological University in Singapore. "The purpose of his site is to polarise and radicalise people so that they become ripe for recruitment."
In 2010, Mr Abdul Rahman was sentenced to five years in an Indonesian jail for concealing information related to the terrorist attacks at the JW Marriott and Ritz-Carlton hotels in Jakarta, which killed seven people and injured about 50. He had arranged for $10,000 in cash to be passed to the main bomber, according to the US government.
Citigroup said: "We have a number of policies and procedures in place for our vendors designed to help prevent our advertising from appearing on inappropriate sites. In this case we have acted quickly to rectify the issue and have taken steps to ensure our ads will not appear on this site in the future."
IBM said that it was "looking into the matter and will take all measures with its agency buying partners to prevent recurrence".
Microsoft said: "The advertisement was placed using a third-party automated online media buying process and has now been removed. We're working with our media buying partners to identify additional safeguards to further reduce the potential for ad placement on inappropriate sites."
An industry insider who has been gathering data about Arrahmah.com for the Financial Times estimated that the site was making thousands of dollars per month based on its ad traffic, and potentially more.