Noun

1. A duplicate or counterpart of something or someone that acts in a contrary, nefarious, or insidious manner.

   As a ploy to discredit the reformist politician, the opposing party had hired a lookalike to act as his evil twin and be seen in a variety of compromising situations.

   • 2003: Peter Halstead, Sea Sun http://books.google.com/books?vid=ISBN0974716502&id=Ukh0lXxvzgIC&pg=RA2-PA67&lpg=RA2-PA67&dq=%22evil+twin%22&as_brr=1&sig=AD2U5PekR-PcV8POw62deV_QhhE

     ...we see the flip side, the evil twin, the dark side of addition. Human nature contains both a thing and its opposite in varying degrees of tension, and so for every plus there is a minus.

   • 2004: Bob Sullivan, Your Evil Twin: Behind the Identity Theft Epidemic http://books.google.com/books?vid=ISBN0471648108&id=SCf7swqny4MC&pg=PA42&lpg=PA42&vq=%22evil+twin%22&dq=%22evil+twin%22&sig=TJN61bkvb8d6SG1UkJP3cIRzM2s

     ...[he]..lived his life under [another man's name], becoming his evil twin: Staas bought and sold homes, opened bank accounts, obtained credit, married twice, and was arrested at least three times.

2. A rogue wireless access point installed near a legitimate one for purposes of eavesdropping or phishing.

Synonyms

• (duplicate of contrary or nefarious intent): alter ego, changeling, doppelganger