WASHINGTON (AP) — Microsoft Corp., the Hewlett-Packard Co. and other multinational corporations have avoided billions in U.S. taxes by shifting profits offshore and taking advantage of weak, ambiguous sections of the tax code, Senate investigators said Thursday.

Microsoft used “aggressive” transactions to shift assets to subsidiaries in Puerto Rico, Ireland and Singapore, in part to avoid taxes, said the report by the Senate Permanent Subcommittee on Investigations. In one example, the report said that the Washington state-based software giant saved $4.5 billion in taxes from 2009 to 2011 by shifting assets to Puerto Rico, a U.S. commonwealth that offers numerous tax breaks to businesses.