Viveros said there's a growing number of remote access Trojan programs sent via e-mail that can open the backdoor to a user's PC and gather log-ins and passwords to company intranets.

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So far this year, 34% of all malicious Android programs were Trojan spyware programs, with backdoor programs accounting for 31% and SMS Trojans another 27%, according to Kaspersky Lab.

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But probably the most inexpensive full-blown solution comes from Moosoft, which specializes in solutions to Trojan horse programs.

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When word leaked out about a week ago that Sony was using a copy-protection program to keep people from copying their music CDs, music lovers cried foul and security experts warned the XCP copy protection system could be hijacked by so-called Trojan horse programs.

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And even though Microsoft has a feature in its Internet Explorer browser designed to steer users away from unknown and potentially untrustworthy software, about 5 percent of users ignore the warnings and download malicious Trojan horse programs anyway. via Microsoft: One in 14 downloads is malicious.

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Unlike Shields Up, Security Check also scans for approximately 60 Trojan horses, which are malicious programs masquerading as other applications that you might unwittingly download.

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Beginning in late August, for instance, hackers exploited a vulnerability in Java to install nasty programs like the Poison Ivy trojan to PCs.

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