Historically, the vast majority of trojans, worms, and viruses have targeted the (Windows) PC. Attack and propagation methods may have grown more sophisticated, but the PC has remained the focus of most malware. According to a paper written by a team of researchers at Indiana University, however, this could change in the future. According to the team's research (PDF), an attack that specifically targets wireless routers and spreads between them at any point where coverage overlaps could quickly and easily propagate throughout an entire city.
Until recently, such an attack vector was considered unlikely. Wireless routers are inherently less secure than their wired counterparts, but the development of WPA encryption has increased (theoretical) wireless security significantly. More practically, wireless routers weren't deployed in sufficient numbers and didn't overlap their areas of coverage enough to present a significant propagation risk.
Malware, Trojan, Worm, Virus, WiFi, Wireless, Touter, Wireless Router, WPA, Encryption