Mortgage fraud cases under investigation by the FBI have jumped by about 63% in the past year, according to bureau director Robert Mueller.

"The schemes have evolved with the changing economy, targeting vulnerable individuals, victimizing them even as they are about to lose their homes," he told the Senate Judiciary Committee on Wednesday.

The FBI has more than 2,600 cases open, with most of them involving losses of more than $1 million, Mueller said. That's more than triple the number of three years ago and up from 2,400 cases Mueller said were open in May.

The FBI has shifted its investigative resources to focus on mortgage fraud and assigned about 300 special agents to the task. Mueller said their focus has centered on "industry insiders."

The FBI also has more than 580 open corporate fraud investigations, he said. The bureau has declined to identify any companies under criminal probes.