Yep. There’s a hole. Big hole. If you’re using Firefox 3.5, there’s a zero-day exploit in it that will let someone execute a so-called “drive-by” attack on your computer under certain circumstances, according to Tom Espiner at CNET. That means that if you visit a Web site that has malicious code written into it, a hacker may be able to use that exploit to gain access to your computer.

Mozilla said that the flaw lies within the JavaScript just-in-time (JIT) compiler. There’s currently no patch available for the exploit, though Mozilla’s working on one. So what does this mean for you? It means that if you’re running Firefox 3.5, you need to be extra careful where you go at least until Mozilla gets this vulnerability patched. Otherwise, your computer might just pick up something nasty.

You can, if you want, disable the JIT compiler, but Mozilla wants you to know that that’ll decrease the performance of JavaScript.