I have tried many times to change the default search engine back to firefox, google etc.. but it keeps coming back. I know have 2 search engines ! One is 'nuesearch' and the other is 'Lucky123'. I already have BT Antivirus and I have tried to contact BTfor a helpline number but no luck. Not sure what i'm paying for !
Looks like someone may have 'accidentally' let something be installed. Like browser toolbar or some such. Do a search online for hijackthis, it usually sorts out the junk.
Folks really need to be careful what they click on and actually read the info during a software install which often includes 'helpful' browser add on items. Next thing is get yourself a proper antivirus program. The free Avast seems to be recommended. I prefer my paid for Endpoint.