Yes. For instance: all the recent drama about &quot;layering&quot; and &quot;spoofing&quot; fraud is about small (and surprisingly dumb) pieces of code that exist to trick electronic trading systems into trading against their owners interests.<p>As for efficiency: it is sure as shit more efficient than when stocks were quoted in eighths, and market makers had a collusive agreement to not to quote odd eighths so they could pocket extra money.