I would think ordering magazines and planning to cancel them would meet all of the legal qualifications for fraud. Now, on a practical level, individuals who do this for relatively small amounts of miles probably have nothing more to fear than losing the miles, as ananish suggests. However, the amount of miles that ananish mentions is no longer chicken feed: 1 million miles would buy 10 r/t, 1st class tickets from JFK-LHR, which have a value of more than $115,000. That might well be enough to potentially pique the interest of a district attorney who might want to grab a headline about fighting computer fraud.