PNC Bank says only a “small percentage” of customers were affected by a website slowdown caused by a recent cyberattack, the Pittsburgh Business Times reports. The Pittsburgh-based subsidiary of PNC Financial Services Group Inc. (NYSE:PNC) has been dealing with such attacks since September and saw more problems in December and the first part of January, the newspaper reports. PNC said in an email to customers that accounts have not been compromised. “For several weeks, PNC has taken steps…