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.

CNN: New 'Trojan Horse' strain may go mainstream

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.

FORBES: Worm Attacks Coming For Google's Android - Kaspersky Lab

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

CNN: Back Orifice 2000 under control