Apple faces its strongest attack yet, with its iTunes market lead threatened by the launch of MySpace Music, expected to start-up for real in the US this week.

The question on music industry and analyst's lips is, "can the world's largest music-focused social network take a chunk out of iTunes sales?" Some industry watchers, however, remark that the most likely competition to be generated as a result of the launch will be between News Corp's MySpace and CBS' Last.fm.

MySpace last night confirmed itself to have won support from major advertisers to kick-start its free music streaming and paid purchase MySpace Music service.

McDonald's, Sony Pictures, Toyota and State Farm will pay for ads, underwriting the service which is expected to launch for real in the US this week.

MySpace Music offers catalogue from three majors (all but EMI) and some indies (through its deal with Amazon, which is handling the infrastructure for music downloads, which are not free through the service).

Whereas MySpace users can now only add a single song to their profiles for sharing, MySpace Music will allow them to create and post entire playlists.

"With MySpace Music integration, premium brands are offering our users and their customers new ways to discover, experience, and share music online and offline, said Jeff Berman, president of sales and marketing at MySpace."

MySpace Music has been organised as a joint venture with Sony BMG, Universal and Warners. The fact the majors have a slice of the action underscores their desire to topple iTunes from its leading position in digital music retail.

"We haven't made just a commercial deal with the labels, but a joint venture, so they are invested in our success," Berman added.

The service starts without a CEO, but weekend rumours suggest the company may be preparing to hire former Facebook COO Owen Van Natta to the role.