Microsoft is trying to convince customers who have fled the company’s Office software in favour of an open source alternative to return to the proprietary flock by publicly dissing its rival.

But the rival in question, as you might expect, isn’t internet kingpin Google. Instead, Redmond has splashed out on an ad that warns against the use of OpenOffice.org.

Ars Technica spotted a video yesterday on Microsoft’s ‘Office Videos’ YouTube channel, which the company has since yanked.

However, it’s still available via Microsoft.com for those interested in seeing MS defend its product against OOo.

The vid cites customers who struggled with using OpenOffice.org and then went back to using Microsoft’s software.

According to Ars, the company got its quotes from various newspaper reports and case studies published on Microsoft’s corporate website over the past few years.

Indeed the ad itself reminds this reporter of the script MS execs consistently read from when quizzed about the open source competition, so it’s hardly that surprising to see it used as a way of trying to woo customers back to the vendor’s Office suite.

In August 2009 Microsoft was spooked enough by Linux outfits, to go public about its fears. It warned investors about new threats to its precious client-side tech ecosystem, by listing Linux companies Canonical and Red Hat as rivals in its annual Form 10-K filing.

And now, it’s panicking about OOo, too. But by declaring such a threat, it would seem that Microsoft just admitted that it's worried about losing market share in an area where it has been unshakeable for years. ®