A U.S. Senate committee memo said Microsoft Corp. (MSFT) used aggressive international tax maneuvers to avoid billions of dollars in taxes over the past three years.

The report, released in advance of a 2 p.m. hearing in Washington today, said Microsoft used transactions with subsidiaries in Puerto Rico, Ireland, Singapore and Bermuda to save at least $6.5 billion in taxes. In 2008, Hewlett-Packard Co. (HP) created a series of short-term internal loans that allowed the company to tap its offshore cash for domestic operations without paying taxes, according to the report.