seoisabusiness - 9:00 am on Jun 16, 2010 (gmt 0)
please check your logfiles for googlebot request for MBISetup.exe (or more generall .exe stuff)
18.104.22.168 - - [16/Jun/2010:07:15:42 +0200] "GET /ticker/MBISetup.exe HTTP/1.1" 301 99 "-" "Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)"
and what you return to such request (what status code?).
also look for other "maleware googlebot check request" from google and what HTTP status you return for them.
this is a possible lead as there is a major time overlap.