Ask.com - illegal 'capture' of computer

I opened my computer this morning to find my search facility suddenly taken over without warning by ask.com.  I did not ask for this and when asked if I wanted to enable the transfer I clicked 'Don't enable'.  Despite this I suddenly found my computer installing the software for ask.com.  I went to 'Programs' and tried to uninstall it only to be told by Windows that I would need an administrator to do this.  I am utterly outraged.  How dare ask.com interfere with the system as I have chosen to set it up!  Who do these people think they are?  And how dare any company install software on my computer which I know nothing about, have clearly stated I don't want and am unable to remove when I want to.  No reputable company would behave like this.  I cannot see any difference between this is and hacking into a mobile phone.