To carry out the massive accounting fraud at Indian outsourcer Satyam, the perpetrators used the tool with which they were most familiar -- information technology.

Former chairman Ramalinga Raju, along with his alleged accomplices, created a complex system of business applications in order to generate thousands of fake invoices that were used to falsely inflate the company's revenue by more than $900 million, investigators said Monday.

"The investigation revealed that in order to perpetrate this fraud, the accused have surreptitiously got a subroutine incorporated into the source code of the [Invoice Management System]," India's Central Bureau of Investigation said in a statement.

The system was set up so that the perpetrators could log in as a so-called "Super User" to create fake documents that would not be detected by Satyam's legitimate business applications, according to the CBI. They also allegedly used a modified version of Microsoft Excel linked to the IMS to bypass Satyam's accounting controls.

All told, Raju and his cohorts -- including, allegedly, two employees of Satyam auditor PricewaterhouseCoopers India -- used the setup to create 7,561 phony invoices purportedly worth $946 million.

CBI investigators engaged forensic computer analysts to help uncover the scheme. "As a result of this detection, the actual modus operandi as well as the individuals who have perpetrated the fraud have been identified," the CBI said.

Raju was arrested and jailed earlier this year for his role in the scandal. Telecom outsourcer Tech Mahindra has agreed to acquire Satyam for $422 million in an effort to give the company a fresh start.

Last week, Raju's attorneys claimed that he's suffering from cardiac problems that render him unfit to take lie detector tests that authorities hope will help them uncover more details of the fraud.

Raju's legal reps made the claim in responding to the CBI's request that Raju make himself available for polygraph testing, according to India's Business Standard newspaper.

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