Wells Fargo (WFC) weathered a cyberattack on Tuesday that left some of the company's customers unable to log in to their accounts.

The nation's fourth-biggest bank by assets experienced "an unusually high volume of website traffic which we believe is a denial of service attack," spokeswoman Sara Hawkins said in an email.

Hawkins said the "vast majority" of Wells Fargo's customers were unaffected by the electronic assault, which disrupted online and mobile banking. The company encouraged customers who were unable to access their accounts "to try logging on again as the disruption is usually intermittent," Hawkins added.

The website Sitedown.co on Tuesday afternoon logged roughly 184 reports of people being unable to log in to their accounts at Wells Fargo within the preceding 24 hours compared with 195 such reports in the past seven days.

Earlier Tuesday, the al-Qassam Cyber Fighters, a hacktivist group that has claimed responsibility for a series of attacks since September that have bogged down websites at some of the nation's biggest banks, claimed in an email to have barraged websites at Wells Fargo, JPMorgan Chase (JPM), BB&T (BBT), PNC Financial (PNC), Citigroup (NYSE:C), U.S. Bancorp (USB), SunTrust (STI) and Fifth Third Bancorp (FITB) in the past week. The group vows to continue its campaign until YouTube takes down a trailer for an anti-Muslim film.

The attack on Wells Fargo comes five days after a denial of service attack on TD Bank that rendered mobile and online banking systems at the Toronto-based bank inoperable. Key Bank in Cleveland, Ohio endured a website outage on March 19, the website BankInfoSecurity reported. Key Bank spokeswoman Lynne Woodman said in an email the bank was "not affected" by a cyberattack although she otherwise did not comment on the report.

Both JPMorgan Chase and BB&T confirmed recently they had endured denial of service attacks.

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