Seth Wenig, Associated Press
In this file photo, a person walks past a Citibank branch in New York. The websites of major banking companies like Citigroup have been disrupted in recent weeks by distributor denial-of-service attacks.

As cyber attacks on online banking sites continue, PNC Bank apologized to customers who have been adversely affected by the bank’s efforts to stop these attacks, according to an article by The Tribune Live.

But the good news for customers is that these attacks have little effect on them, other than sometimes preventing them from accessing banking sites, according to an article by NBC news.

Attacks started earlier in the fall but started again in December. Several large banking companies have been affected by what is called a distributed denial-of-service attack, including Wells Fargo, KeyCorp and U.S. Bank.

"There is nothing an organization, a bank, a newspaper, or anyone can do to prevent attempts to phish or hack or do denial-of-service attacks," said Key spokeswoman Lynne Woodman in a article.

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"But customers do not need to be afraid for the safety of their money," Woodman said. "The banks are turning themselves inside out to keep people's money safe."

These attacks haven’t accessed personal information from the sites.

In this type of attack, a website is flooded with high-volume traffic from the attackers, which the bank tries to block. This creates shutouts for a “small percentage of legitimate ... customers for an extended period,” as PNC said to Fox Business.

A group offended by a video mocking the Muslim prophet Muhammad has claimed responsibility for the attacks, according to the Cleveland article.