"I was spending time every week trying to keep the machine free of viruses and worms," said Mr. Tucker, a vice president of Salesforce.com, a Web services firm based here. "I was losing the battle. It was cheaper and faster to go to the store and buy a low-end PC."

In the face of a constant stream of pop-up ads, malfunctioning programs and performance slowed to a crawl or a crash -- the hallmarks of spyware and adware -- throwing out a computer "is a rational response," said Lee Rainie, director of the Pew Internet and American Life Project, a Washington-based research group that studies the Internet's social impact.

While no figures are available on the ranks of those jettisoning their PC's, the scourge of unwanted software is widely felt. This month the Pew group published a study in which 43 percent of the 2,001 adult Internet users polled said they had been confronted with spyware or adware, collectively known as malware. Forty-eight percent said they had stopped visiting Web sites that might deposit unwanted programs on their PC's.

Moreover, 68 percent said they had had computer trouble in the last year consistent with the problems caused by spyware or adware, though 60 percent of those were unsure of the problems' origins. Twenty percent of those who tried to fix the problem said it had not been solved; among those who spent money seeking a remedy, the average outlay was $129.

By comparison, it is possible to buy a new computer, including a monitor, for less than $500, though more powerful systems can cost considerably more.