A computer virus that may leave Microsoft Windows users vulnerable to digital hijacking is spreading through companies in the U.S., Europe and Asia, already infecting close to 9 million machines, according to a private online security firm. Fortunately, however, it may be a dud. Though computer bugs have become a common affliction, Finland-based F-Secure says a virus it has been tracking for the past several weeks has surged more rapidly through corporate networks than anything they’ve seen in years.