Support for Windows XP ends on April 8th, 2014. Tim Rains of Microsoft goes over the risks of running the operating system after support ends. Running the OS after that date is definitely not something that I would really trust. So, for you still running it, it might be getting time to update your PC.
Some of the people I have discussed this scenario with are quick to point out that there are security mitigations built into Windows XP that can make it harder for such exploits to be successful. There is also anti-virus software that can help block attacks and clean up infections if they occur. The challenge here is that you’ll never know, with any confidence, if the trusted computing base of the system can actually be trusted because attackers will be armed with public knowledge of zero day exploits in Windows XP that could enable them to compromise the system and possibly run the code of their choice. Furthermore, can the system’s APIs that anti-virus software uses be trusted under these circumstances? For some customers, this level of confidence in the integrity of their systems might be okay, but for most it won’t be acceptable.