Thanks so much Vger. The spider "search" is the fifth one listed - it is a bit hidden at the top of the list with a few that are not sorted alphabetically. I think I have figured out a solution to my problem. I went to www.my-addr.com and looked at the user-agent information for each of my browsers. The only 2 browsers this happened with were IE8 and Firefox. I noticed that they both had entries in the user-agent field that contained the word "search". Did a little research online about the "MindQuizSearchToolbar 1.1" and found that it is a non-malicious adware toolbar put out by Zugo, ltd. that attaches itself to a browser. I was unable to remove it in IE using Tools>Manage Add-ons>Toolbars and Extensions (be sure Show>All Add-Ons is selected) because the option to delete it was grayed out (funny!). I was able to remove it in the Windows Control Panel>Programs and Features area though. It was simply called "Search Toolbar" there. Once removed, I rechecked the IE8 User-Agent info at www.my-addr.com and the string "MindQuizSearch Toolbar 1.1" was gone. Now the customer can login to my store with the default list of spiders and Prevent Spider Sessions = True. This process did not fix the issue with Firefox however. It looks like it's user-agent string "MindQuizSearchToolbar/1.2" refers to a toolbar add-on called "Torrent Finder Toolbar" but as of yet I haven't been able to find it on my system to remove it. I will post my steps when I get it figured out.

IE 8.0:
Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; WOW64; Trident/4.0; MindQuizSearchToolbar 1.1; GTB6.6; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.5.21022; .NET CLR 3.5.30729; .NET CLR 3.0.30729; InfoPath.2; .NET4.0C)

IE 8.0 after Search Toolbar removal:
Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; WOW64; Trident/4.0; GTB6.6; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.5.21022; .NET CLR 3.5.30729; .NET CLR 3.0.30729; InfoPath.2; .NET4.0C)

Firefox 3.6:
Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 ( .NET CLR 3.5.30729; .NET4.0C) MindQuizSearchToolbar/1.2

Firefox 3.6 after Search Toolbar removal (no change, still working on it!):
Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 ( .NET CLR 3.5.30729; .NET4.0C) MindQuizSearchToolbar/1.2

Safari 5.0:
Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/533.19.4 (KHTML, like Gecko) Version/5.0.3 Safari/533.19.4

Google Chrome 8.0:
Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10

Opera 9.80:
Opera/9.80 (Windows NT 6.0; U; en) Presto/2.7.62 Version/11.00