"Smartphones such as the iPhone and Android-based handsets, which are used increasingly for business purposes, are essentially miniature personal computers, and in 2010 will face the same types of attacks that target traditional computing,"
Information Week has a decent list of what security experts are predicting will be this year's top security challenges.
I think the bot nets and organized crime aspects are the most worrisome. Network spreading malware infects unprotected computers, which can then be controlled remotely to instigate DDOS against common targets. Of course this isn't new but I worry when the people behind the bot nets become organized and politicized.
As the quote above indicates, another hot topic in security is going to relate to Smart Phone apps. How much security is built into your Smart Phone and its application marketplace?