Few phrases get financial journalists’ pulses racing more than ‘the Pac-Man defence.’ Named after the 1980s video game, it involves the target of a hostile takeover bid turning around and launching its own bid for its unwelcome acquirer.

News on Friday that Nasdaq OMX had teamed up with Atlanta-based IntercontinentalExchange to launch an $11.3bn bid for NYSE Euronext was inevitably met with speculation that NYSE Euronext might rebuff the approach and launch its own bid for Nasdaq - that is, do a Pac Man.