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(CNN) - A new study finds nearly a quarter of malware on mobile devices comes from porn websites.

The study was conducted from Blue Coat, a web security and optimization company.

Mobile users don't check out porn sites often, less than one percent of all mobile traffic is pornography. But when they do go to those sites, the risk of inadvertently downloading malware to their devices increases three-fold.

That makes watching porn on smartphones a far bigger threat than viewing porn on a PC.

Porn led to more malware on smartphones and tablets than e-mail spam, malicious websites and fake apps combined.