New York Attorney General Eliot Spitzer sued a major Internet marketer Thursday, claiming the company installed “spyware” and “adware” that secretly install nuisance pop-up advertising on screens, which can slow and crash personal computers.

Spitzer said the suit filed in New York City against Intermix Media Inc. of Los Angeles combats the redirecting of home computer users to unwanted Web sites and its own Web site that includes ads, the adding of unnecessary toolbar items and the delivery of unwanted ads that pop up on computer screens. After a six-month investigation, Spitzer concluded the company installed a wide range of advertising software on countless personal computers nationwide.