Hi, first let me suggest that you should think of some less complicated way of displaying the data. I guess you could achieve the same result with just about twenty lines of code.

But to answer...

check for viruses:

your hosting must be allowed to execute files (which I seriously doubt)
you have to know where the antivirus program is and what parameters it expects
then use exec() to...

All right, I can see that you know what you're doing :-)

Since your hacking it anyway, we won't mind using eval(), will we? (yuck!)

$string = "level1.level2a.level3=10";

list($combinedKey,...

I agree with forzadraco: don't do this.
An attacker could simply call your page with:
page.php?string=;DELETE * FROM yourtable
and you're dead.

However, to answer your question, the function...