You got a virus/trojan/malware doing that.
buy and install an antivirus or run the antivirus for free from one of these two locations:
http ://housecall.trendmicro.com/ (this is trend micro's)
http:/ /www.microsoft.com/Security_essentials/ (microsoft's)
oh...so you have an apple....then you are in the wrong category...I'll transfer you and opt out.