Claria's software, for example, usually isn't listed by name in the "add/remove programs" menu on computers, making it harder to delete. And users who click on ads for Claria products see installation screens that don't say what will happen to their computers until after the user indicates that they accept.
Claria Chief Marketing Officer Scott Eagle said the company had recently made its terms clearer and its removal easier.
Claria competitor 180Solutions makes pop-up software that is installed automatically through browser security holes. Although the firm said it was cracking down on that practice, it still offers bounties for each installation, a model that analyst Stein said encourages "all kinds of sneaky tactics." Recent 180Solutions ads ran on behalf of J.P. Morgan Chase and Disney.
"Most of their advertisers are mainstream companies," said Ari Schwartz, associate director of the Center for Democracy and Technology, a nonprofit public policy group.
Just as not all merchants care how they get their business, not all affiliate networks are equally strict. Take Commission Junction, which is owned by Westlake Village-based ValueClick Inc. and drives computer users to Citigroup Inc.'s Citibank, Home Depot Inc. and IBM Corp.
Until this month, Commission Junction's 70,000 affiliates included 180Solutions and a firm called Exact Advertising, which makes a "Bargain Buddy" pop-up that has been installed through a security flaw in Web browsers. Bargain Buddy recently carried ads for 1,000 merchants, including Dell Inc., British Airways and Gap Inc.
After The Times asked about the practices of Exact Advertising and 180Solutions, Commission Junction said it was going to stop doing business with both.
Some say fed-up computer users are the ultimate police force. Dell, the world's largest maker of personal computers, withdrew its advertising from the biggest adware companies a year ago. It quit working with Exact Advertising last month after customers complained.
When Dell's anti-spam or anti-spyware policies are abused, Dell spokeswoman Jennifer Davis said, "if we don't find out about it, a customer is going to tell us." But others, including Lurhq's Stewart, don't think consumers understand enough about what's going on to pressure the blue-chip firms.
Far from fighting back, he said, "before long, they'll start to think the Internet is supposed to have pop-up ads on every page."