Hello Michelle,
Two points:
1. The word "malware" is short for "malicious software." It's a broad
classification that includes viruses, trojans, spyware and adware,
etc.
2. Anti-malware programs come in one of two types--anti-virus and
anti-spyware and adware. No single program really does both.
There is not one product that can trap every virus / spyware /
trojan. You should consider getting MalwareBytes' Anti-Malware Free
and SuperAntiSpyware free as additional tools.
Windows Defender detects and removes known spyware only. It is not designed
to protect against the full breadth of malicious software, and specifically
does not prevent viruses, worms, Trojans, and other malicious software from
infecting your machine.
Microsoft Security Essentials real-time protection, including anti-virus,
anti-rootkits, anti-Trojans and anti-spyware. (and is free)
-=-
