The 24-year-old from Liverpool claimed she was raped after visiting one of the men at his home in Bolton, after making contact on the internet.
But the trial at Preston Crown Court collapsed when computer evidence was produced showing her entertaining the prospect of group sex.
Judge Robert Brown ordered the jury to return not guilty verdicts.
Prosecutor Michael Leeming told a jury the case involved allegations of rape and conspiracy to rape at a house in Great Lever, Bolton, on 19 June.
But he formally offered no evidence after reading excerpts of MSN chatlogs of her conversations before the alleged offence.
He said: "It is right to say that there is material in the chatlogs from the complainant, who is prepared to entertain ideas of group sex with strangers, where to use her words 'her morals go out of the window'.
"This material does paint a wholly different light as far as this case is concerned.
"We take the view that it would not be appropriate to offer any evidence."
Judge Brown ordered the jury to return not guilty verdicts for rape and conspiracy to rape against five men.
They were: Kelvin Chinakwe, 26, of Brook Hey Avenue, Bolton; Olatunji Owolabi, 28, of Bradbourne Close, Great Lever; Afolabi Sanyaolu, 29, of Laburnum Road, London; Senthil Venkatachalam, 30, of Wigan Road, Deane, Bolton; and Funsho Bello, 26, of Atherstone, Rochdale.
A sixth man - Ganiyn Conteh, 32, of Abbeywood Avenue, Abbey Hey, Manchester - was formally cleared of conspiracy to rape.
The woman said she had agreed to visit Mr Owolabi after meeting him on MSN.
She alleged she wanted to just have sex with him, but was then raped by the others.
Judge Brown told the jury: "This case depended on the complainant's credibility.
"Not to put too fine a point on it, her credibility was shot to pieces."