"The age-old canards about Jews and money are always just beneath the surface," said Abraham Foxman, the national director of the Anti-Defamation League (ADL), which fights anti-semitism.
"As we witnessed after 9/11, whenever there is trouble or uncertainty in the economy or world events, Jews become the scapegoats and ugly anti-semitic canards are given new life."
The ADL said it had witnessed "a dramatic upsurge" in anti-Semitic statements on online discussion boards, and Internet service providers were struggling to delete them.
Blogs devoted to conspiracy theories as well as white supremacist and neo-Nazi websites have sought to exploit events on Wall Street and the subprime crisis to support their agendas, ADL said.
Referring to the demise of Wall Street bank Lehman Brothers, one poster on white supremacist website Stormfront wrote: "I would imagine the likelihood of the Fed etc bailing the company out depends largely to what degree it is Jewish owned," according to ADL.
Lehman Brothers went bust, while a number of other financial institutions from home loan providers Freddie Mac and Fannie Mae and insurer AIG were nationalized by the US government.