裝了某 extension?
http://www.ekoob.com/how-to-remove-...h-engine-10603/
如果不只有 extension, 可能還有某些 windows 的程式?
http://www.seasonsecurity.com/how-d...ownloader-95061

這兒有人說是 PDF Download 裝上的:
http://ask.metafilter.com/170298/Fi...How-do-I-rescue