If I’m keeping track correctly, I’ve been asked this same question seven times since I started running this website. In fact, I asked myself this question a few years ago: “why does my computer tell me it may be a risk every time I start my PC?” Now, I could drag this guide out and try and sound really smart; however, I want to keep this simple.
The reason your computer tells you it might be at risk when you first turn on your PC is because your anti-virus software has not loaded yet. As such, windows XP (the offender here) jumps the gun a little and assumes you have no anti-virus software on your computer. When your anti-virus software loads, this notice goes away and everything is back to normal again.
This is a classic case of trying to be proactive with security and your computer getting a little too far ahead of itself.
If, however, your PC constantly pops this message up, you should either get a virus checker or, if you already have one, remove it and install Microsoft Security Essentials.