Which is better Spybot Search & Destroy or Lavasoft Ad-Aware SE?

I was wondering if Spybot Search & Destroy blocks spyware from getting into your computer or does it allow spyware to get into your computer and then it deletes it? Does Spybot have active Anti-Spyware shields? same question about Lavasoft Ad-Aware Se, does it have active anti-spyware shields? or does it allow... show more I was wondering if Spybot Search & Destroy blocks spyware from getting into your computer or does it allow spyware to get into your computer and then it deletes it? Does Spybot have active Anti-Spyware shields? same question about Lavasoft Ad-Aware Se, does it have active anti-spyware shields? or does it allow spyware to get into your computer then delete them ? Also, which one is better?
Update: Then is there any free anti-spyware program that have active shields?
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