Tens of thousands of people have downloaded copies of unreleased Leona Lewis songs after hackers stole them from computers belonging to Simon Cowell's record label.

Three tracks from the former X Factor winner's forthcoming album, not due for release until November, were stolen from the television producer's entertainment firm SyCo and leaked online in one of the highest profile hacking cases the music industry has ever seen.

Illegal copies of the songs have already appeared on popular websites including YouTube, with links to download them on Facebook and Twitter.

The tracks include Don't Let Me Down, a song featuring singer Justin Timberlake that was to be the first single release from Lewis's second, currently untitled, album.

Cowell notified the industry body the International Federation of The Phonographic Industry and police in the US and Europe are investigating.

Jeremy Banks, head of the body's internet anti-piracy unit, said in a statement: "IFPI is working with SyCo and law enforcement agencies in the US and Europe to trace the individuals who stole the Leona Lewis/Justin Timberlake track.

"Such pre-release leaks, however they are sourced, are highly damaging to our members who invest considerable budgets in marketing and promoting music ahead of release."

A spokesman for SyCo said its computers had come under a "sustained attack" and added: "We will certainly look to bring charges against those who are responsible."

Lewis, 24, from Hackney, became an overnight sensation when she won The X Factor in 2006. Her debut album Spirit topped album charts all over he world. The next album is expected to include collaborations with singers Ne-Yo, will.i.am and Jay-Z.

Sony BMG, Syco's parent company, has insisted that the leaked songs are demo versions and are far from complete. On YouTube, several versions of Don't Let Me Down have been posted accompanied by a still picture of Lewis.

One user, under the name "NewMusicLeaked1", posted the song three days ago. It has been viewed nearly 20,000 times. Hackers can steal music by infiltrating emails and software using Trojan viruses with codes that bypass security software.

The case comes just weeks after fellow X Factor winner Alexandra Burke also fell victim to online hackers when unfinished tracks from her upcoming debut album were leaked.

thisislondon.co.uk