An Islamic extremist hacker group appears to have followed through on its latest threats to attack several major American banks in retaliation for what it says is “widespread and organized offenses to Islamic spirituals and holy issues.” The attack is one in a series that began this fall under the banner of Operation Ababil, which the group has vowed to continue until the “Innocence of Muslims” film has been removed from the internet.

In several messages it posted to the popular Pastebin text sharing website, the Izz ad-Din al-Qassam Cyber Fighters group has previously warned that it would be targeting American banks U.S. Bancorp, JP Morgan Chase & Co, Bank of America, PNC Financial Services Group, and SunTrust Banks. In October, it laid out a schedule of its planned attacks after successfully hitting Bank of America and JP Morgan Chase the prior month.

On Monday, the Izz ad-Din al-Qassam Cyber Fighters posted a similar threat and announced it was launching Phase 2 of the operation.

PNC Bank confirmed on its Facebook page Wednesday that it was experiencing “an unusual volume of internet traffic,” which was impacting its customers’ ability to access their accounts. On Tuesday, it had posted the following warning:

PNC is aware that some U.S. banks may be the target of a potential cyber attack. There are NO reported system issues at PNC at this time. However, this potential threat could result in high volume of electronic traffic that may make it difficult for our customers to log onto online banking. Please be assured that PNC’s website is protected by sophisticated encryption strategies that shield customer information and accounts. We have no information regarding timing, duration or intensity of this potential threat. Please continue to follow our page for additional updates.

Numerous experts have widely agreed that the attacks are distributed denial of service attacks (DDoS). Such an action simulates many computers visiting a website all at once to overload the site’s servers, essentially rendering the site unavailable due to the excess volume of traffic.Typically this is done via a tool, or an automated script, that can simulate multiple users from an individual computer.

Multiple security researchers interviewed by FOX Business say that the method being executed by the Izz ad-Din al-Qassam Cyber Fighters appears to be more advanced.

“These guys are pretty sophisticated in their understanding of the way the Internet and cyber defenses work,” said Rodney Joffe, senior vice president and senior technologist at Neustar, who has been monitoring the attacks.

Joffe said the attackers have developed their own botnet. Instead of compromising tens of thousands of personal computers, which is often the case, they have focused on taking over Web servers to do the work. These machines either host websites that users visit or push content out to other servers.

Echoing that view, Dan Holden, director of research for Arbor Networks’ security engineering and response team said the attacks “demonstrated a combination of technical and media relations sophistication.”

Another security expert, Michael Smith of Akamai, also indicated that a prior attack “[was]sn’t consistent with what hacktivists are capable of” and that the uniformity of the attack pattern “does not happen with a hacktivist mob.” Smith explained that the volume of traffic simulated in the earlier attacks on the banks was “60 times greater” than that typically launched by ordinary hacktivists in a standard DDoS attack.

The Izz ad-Din al-Qassam Cyber Fighters however, have expressed differently in their admission of methods and motives.

Flashpoint Partners conducted an exclusive interview with the hacker group in November, in which it disputes that it is attacking web hosting companies and internet service providers. The group challenged such conclusions by stating, “Many of [the] technical comments during the attacks have made us doubtful about [the] technical competence of American companies’ security consultants.”

The Izz ad-Din al-Qassam Cyber Fighters also denied in that interview having any connection to Iran, any other government, or to Hamas (The Izz ad-Din al-Qassam Brigades is the name of the armed wing of Hamas). They stated that some want to portray their actions as political and accused such people of “deflecting the issue to the side of their political leanings.”

When asked by Flashpoint Partners why the hackers specifically selected America’s banks as their target of retaliation for insulting the Prophet Mohammad, Izz ad-Din al-Qassam Cyber Fighters indicated that banks represent something that they believe Americans value more than religion.

We have selected the banks because we should have done something proportional to what has happened against us. In the system where…religion and sacred things are not honorable, and only material, money and finance have value, this seems a suitable and effective…act[ion] and can influence governors and decision makers.

In its October post to Pastebin, Izz ad-Din al-Qassam Cyber Fighters had this to say to America, should anyone insult the Prophet Mohammad:

But yes! Although you are nothing and worthless, you have something which is much respected for you. You hold it very dear and without it, life has no meaning for you: Capital, material and money.

Money is all your respect. Money is all your holiness. Money is all of your value. Money is all of your glory. Money is all your humanity. Money is all of your life. Money is all of your honor. Money is all your existence. Money is everything for you.

The group promises to continue its Operation Ababil until the “Innocence of Muslims” video is removed from its online existence.