How do I know if my computer has been hacked?

Okay, this is a repost. But I need an answer and that's why I am posting it again.

I heard that there are large networks of hacked computers or bots and that at least 10,000 are added worldwide everyday!

This makes me think of two questions:

1] Can we rely on a free anti-spyware program like Spybot-Search%26Destroy and a free anti-virus program like Avast if they can be kept up to date? Or can malware be installed on your computer even in the presence of these programs?

2]How do I know if my computer has been turned into a bot or hacked before much of the damage is done? And how do I recover my computer from the hacker's clutches?

Please do not write some funny answers as this is no funny question. Thanks!

How do I know if my computer has been hacked?spyware removal

1 - No, we cannot rely on those tools. Many tools are helpful, yes, but no tool is ever 100% effective. The most powerful tool is common sense. Ie. don't go clicking on spam/popup/chain email links, don't run programs from email or downloads unless you're 100% certain of what it is and what it does, etc. Nothing too mind-blowing.

2 - Many people seem to think slow computers or random errors are sure signs of being "hacked" or "infected". But the truth is, the majority of these cases are really just errors or problems in the system (many times, from the user installing a bunch of crap software; and in some cases, a bunch of crappy, redundant, or even malicious security software). The whole idea of attacking a PC is for that attack to go unnoticed. So in other words, there are really no sure signs of being infected or "hacked", since the best attacks are designed to not be detected (if they're not detected, they can't be fixed).