|probably work of some infection, like virus or something.|
i suggest you to reinstall that particular software.
like if it was IE7:
go to download page of IE7 from MS's website.
in case if that isn't available there you can try at other websites. search using
yah for additional older versions of software you can look on at:
i hope it helps.
yeah, obviously scan for viruses too and delete all the files that could not be repaired.
All the Best! :)