The attacks redirect victims to a website that asks confirmation of user name and password and then displayes a fake live chat support window.
The live chat message appears to be from the fraud department of the victim's bank and asks them to validate their account by entering some contact information.
Fraudsters then collect further information about the victim such as name, phone number, email address and answers to questions used for customer authentication.
These details may enable online or phone fraud against the victim's account, according to the latest monthly report by the RSA anti-fraud command centre.
A US-based financial institution has fallen victim to the attack, but the report said users of all online banking sites should be wary of similar chat activity.
The attack, dubbed "chat-in-the-middle", is hosted on a network associated with a wide variety of cyber criminal activities, the report said.
The network, known as a fast flux network, use peer-to-peer technology to change the location of command-and-control servers continually to avoid detection by law enforcement authorities.
The live chat tactic ensures that cybercriminals receive compromised information in real time, increasing opportunities for attack, the report said.
The number of phishing attacks for August broke the previous monthly record of 15,000 set in April 2008 to reach an unprecedented total of 16,164.
Standard phishing attacks increased only 2% in August, compared with a 38% increase in the number of fast flux attacks, RSA researchers found.
The sharp spike in fast flux attacks in August led to a 22% increase in the overall number of phishing attacks in July, the report said.