The tactics of hackers, cyber-criminals and state-sponsored spies are evolving so quickly that attackers often can re-enter a company\'s networks after being detected and banned, according to a United States computer security firm. Aerospace and defence companies were targets in 17 per cent of sophisticated computer attacks during 2012, the most of any industry, according to a report released yesterday by Mandiant of Alexandria, Virginia. Energy, oil and gas companies were next, with 14 per cent of incidents, followed by the financial industry, with 11 per cent. Most corporate victims — 63 per cent — didn\'t detect intrusions themselves and were notified by security consultants, business partners or other outside entities, Mandiant said. The Mandiant report lists four primary tactics attackers use: subverting information-technology contractors; extensive reconnaissance of networks; persistent pursuit of targets; and installing malicious software on websites visited by employees. Mandiant didn\'t identify groups behind attacks or companies targeted. Bloomberg News