Matthew Clark writes a rational overview of BYOPC on his Confessions of an IT Manager blog, addressing the benefits and concerns of such schemes. One of his concerns is naturally security:
To be clear, there are many possible security issues and implications with BYOPC. These include virus and malware issues, installation of unknown software packages, secure access to business data, and so on. However, I believe all of these issues can ultimately be resolved or mitigated with a well constructed security model.
In conclusion however, Mark writes that the concerns he addresses in the article can be managed and if properly managed, BYOPC could bring advantages in some environments, but is not convinced that BYOPC will necessary reduce costs.
Also in a recent report, Gartner suggests that BYOPC can increase the threat of botnets.