The waves of spam flooding into inboxes are beginning to turn people off e-mail, a study has found.
Many puzzled by how to deal with spam
Some 25% of people said they were using e-mail less because they were receiving so much junk, according to US think tank Pew Internet.
But there were signs that spam works, with enough Americans taking up offers in unsolicited e-mails to justify the cost of sending thousands of messages.
More than half of all e-mails are estimated to be junk.
"People just love e-mail, and it really bothers them that spam is ruining such a good thing," said Deborah Fallows, Senior Research Fellow at the Pew Internet and American Life Project and author of the report.
"People resent spam's intrusions. They are angered by its deceptions and they are offended by much of the truly disgusting content."
For the survey, the researchers interviewed 1,380 internet users in June.
The findings suggest that the recent big increase in junk messages is undermining the popularity of e-mail.
Some people said they were cutting down on their use of e-mail, while about half said they were less trusting of the internet.
The number of unsolicited messages is also affecting how people feel about the net. Just over two-thirds said being online was unpleasant or annoying because of spam.
But the most distress was caused by pornographic messages. Most parents and women were bothered by the fact that explicit images would appear in their inboxes and that they could seemingly do little to stop them.
"The general findings are striking, but inside the data are even more disturbing details about the reactions women and parents have with pornographic spam," said Dr Fallows.
"Pornographers deserve a special place in hell as far as women and parents are concerned."
Just hit delete
Leading companies such as Microsoft, Yahoo, and America Online have stepped up their efforts to stop spam and more and more governments are introducing legislation against unsolicited messages.
At a personal level, the most popular way of dealing with spam appeared to be hitting the delete button, with only a minority using filters to block the messages.
52% trust e-mail less
76% bothered by obscene or offensive content
75% bothered that they cannot stop the flow of spam
33% have clicked on a link in an unsolicited e-mail
Perhaps more surprising, the researchers found that unsolicited e-mails actually work.
A third said they had clicked on a link in a spam message to get more information, while 7% said they had ordered a product or service advertised.
The percentage of junk messages has grown at a phenomenal rate over the past 12 months
A year ago, spam accounted for just 2.3% of all e-mails, according to experts. By May this year, the figure was 55%.