Adware is a malicious software program which shows up unwanted ads on a computer where it is installed. The ads are unsolicited and shows up without the consent of the user.
BHO stands for Browser Hijack Object. BHO hijacks the home page of the default internet browser of the compromised system, so if a user opens the browser to surf the web the BHO automaticually redirects the user to unwanted websites.
Malware is a malicious software which disrupts the computer operations.
Spyware is a program written and distributed by hackers which steals information from the infected computers.