Half of businesses have incurred costs in helpdesk support time, disrupted business activity and reduced productivity because of spyware infections, a survey of more than 600 companies has found.
The survey, by anti-spyware software provider Webroot, found that more than a quarter of firms had lost confidential information through spyware on their networks.
Victims include US retailer TJ Maxx, which is fighting lawsuits following reports that hackers were able to steal customer credit card details through an infected PC.
In another case, multiple businesses were infected with spyware after staff visited an adult website which downloaded malicious code onto their work computers.
An analysis of 250 million websites by Webroot found that three million were infected by spyware.
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