World biggest Prime Number found using Windows XP?

Whilst on the train into London this am I was browsing Metro and spotted this story

13-million digit prime number discovered

‘The University of California, Los Angeles team found the number, which is too long to appear on this page, on a network of 75 computers running Windows XP.’ (my bolding)

UCLA academics yesterday said that while the prize cash was nothing special, the 'bragging rights' would be terrific.’

Keith Coombs - has a little more info

Rob