Banks and other financial firms are facing a barrage of cyberattacks that aim to temporarily disrupt their websites and apps, primarily driven by a surge in so-called hacktivists who target companies in geopolitical hot spots.

Hackers are using new and more aggressive tactics to take down or slow access to companies’ websites and online services. The hacks, typically considered a low-level nuisance, can be damaging for banks that need to be accessible all the time, said Teresa Walsh, global head of intelligence for the Financial Services Information Sharing and Analysis Center, a non-profit that facilitates the sharing of information about cyber threats among financial firms.