Hackers are finding new ways to attack unknowing computer users by taking advantage of weaknesses in Web applications and browser plug-ins, sometimes turning even legitimate Web sites into a source of malicious code, according to a report issued by Symantec, the Cupertino security software company. In another trend, security experts are noticing a significant proliferation of Internet worms and other malicious activity in nations with "emerging economies," where increasing computer use has been accompanied by widespread adoption of pirated software that lacks updated security protection.