...executable and stopped working.

I got this like, 5 times when I was just randomely surfing the web, and I have no idea what I did, the only executable thing I changed lately was my Firefox add-ons. I was thinking maybe it was the ESET Smart Security 4 I installed yesterday, but I installed that pretty early in the afternoon and used the comp alot, in which nothing relating to the Racagent appeared, any ideas o.o"?