Iran is being blamed for a recent wave of cyberattacks, namely a series of Distributed Denial of Service attacks launched against major financial institutions. Affected financial institutions include, but may not be limited to, Bank of America, Chase, Citigroup, Wells Fargo, HSBC, Capital One, PNC, U.S. Bancorp, Fifth Third Bank and BB&T.

Although it is often very difficult to say with absolute certainty that a particular person, place or organization is responsible for such attacks, various officials and experts are convinced Iran is behind the attacks. A group who identifies itself as the Izz ad-Din al-Qassam Cyber Fighters has also claimed responsibility for the attacks, but intelligence officials suggest the group is most likely a cover for Iran.

"The scale, the scope and the effectiveness of these attacks have been unprecedented," said Carl Herberger, vice president of security solutions at Radware, a security firm that has been investigating the attacks on behalf of banks and cloud service providers. "There have never been this many financial institutions under this much duress."

Source: New York Times

Effective DDoS attacks result in major service interruptions, but such attacks do not necessarily constitute a breach in security – accounts, data and financial information should remain safe. DDoS attacks are often carried out by enormous networks comprised of thousands of computers which concurrently target a particular network, eventually overwhelming the capacity of their servers.
Such attacks are typically performed without any sort of network or system intrusion, but even so, may still be very difficult to defend against without interrupting services for regular users. In this case, attackers have upped the sophistication of their DDoS operation by possibly hijacking data centers and flooding banking sites with intractable quantities of encryption requests. This has increased the efficiency with which attackers have been able to cripple their targets.
Some officials strongly believe Iran is retaliating against the recent revival of a highly sophisticated malware threat and tightening U.S. sanctions. The resurfaced malware, Stuxnet and Flame, were specifically designed to create problems across Iran's government systems. The U.S. and Israel are largely credited for the creation of these cleverly-written, troublemaking viruses.