Microsoft will begin testing a free version of its Works software that displays adverts as the company tries to battle back against Google's free online office tools.

Microsoft Works usually sells for $39.99 (£19.60), but the company plans to partner with computer manufacturers and install it on Windows PCs for free.

Works will display a cache of adverts that are stored on a PC, with adverts being updated when a computer is connected to the internet.

Melissa Stern, a senior product manager in Microsoft's Office group, said the test run with Works would let Microsoft see if the ad-supported business model could be extended to other software.

Microsoft Works includes basic spreadsheet and word processing software, but it has faced stiff competition since the launch of Google Docs & Spreadsheets.

Microsoft said it plans to roll out the free version of Works in the next few months, but didn't disclose which PC makers would be taking part in the initial tests.