Google Inc stepped up its assault on Microsoft Corp's productivity software business with the acquisition of a small start-up company that allows Microsoft users to edit and share their documents on the Web.

Microsoft Corp CEO Steve Ballmer intends to keep the regulatory heat on Google as his company strives to lessen its rival's dominance of Internet search.

Microsoft has issued a new software download that will let European users of Windows operating system decide if they wish to keep Internet Explorer as their computer's default browser, the company said on Monday.

Microsoft Corp made its most vehement and public attack on Google Inc on Friday, calling its internet rival's actions potentially anti-competitive, and urging victims to file complaints to regulators.