ALBANY, N.Y. – New York Attorney General Eliot Spitzer sued a major Internet marketer yesterday, blaming it for secretly installing software that delivers nuisance pop-up advertisements and can slow and crash personal computers.

The attorney general’s office also acknowledged that Mr. Spitzer is questioning some of the nation’s biggest banks in an investigation of potential discriminatory practices in setting mortgage rates and fees.

Mr. Spitzer accuses the Internet-marketing company Intermix Media of redirecting computer users to Web sites where ads get displayed, adding unnecessary toolbars to Web browsers, and delivering unwanted ads that pop up on computer screens.

A six-month investigation found that the company installed a wide range of advertising software on countless personal computers nationwide, with more than 3.7 million downloads directed at New Yorkers alone, Mr. Spitzer said.

“Spyware and adware are more than an annoyance,” Mr.Spitzer said. “These fraudulent programs foul machines, undermine productivity and in many cases frustrate consumers’ efforts to remove them from their computers. These issues can serve to be a hindrance to the growth of e-commerce.”

Christopher Lipp, senior vice president of Intermix, denied promoting or condoning spyware, saying its toolbars and redirect applications do not collect personal information on computer users.

According to Mr. Spitzer, Intermix owns and operates such Web sites as mycoolscreen.com, cursorzone.com, and flowgo.com, which advertised screensavers, games, and other software available for download. Though those programs are free, they often carry other software for delivering ads and can interfere with normal computer use, he said.

One of the company’s ad-delivery programs, KeenValue, delivered popup ads while another program, IncrediFind, redirected Web addresses to Intermix’s own search engine, Mr. Spitzer said.

In other news, a source familiar with the “early stages” of an investigation by Mr. Spitzer into possible discriminatory practices involving mortgages said that Citigroup, HSBC Holdings Plc, Wells Fargo & Company, Countrywide Financial, and Norfolk Mortgage have been sent letters regarding the companies’ loan pricing. Mr. Spitzer is also seeking applicants’ credit scores, “loan-to-value ratios,” and any internal reviews by lenders into ethnic disparities of loan trends, said the source, who spoke on the condition of anonymity.

“We are looking at the HMDA [Home Mortgage Disclosure Act] data and other information that would help us understand how the loans are being priced and whether or not they are justified by legitimate business practices,” said Spitzer spokeswoman Juanita Scarlett.

Under HMDA, financial institutions are required to collect and make public information on home loans priced above comparable Treasury rates. First-lien loans must be reported if they exceed the Treasury rate by 3 percentage points, and second mortgages by 5 points.

Community groups looking at the data have concluded that African-Americans and Hispanics are more likely than whites to get higher-costing mortgages. These groups also argue that minority families are much more likely than whites to be turned down for mortgages.