No Matter how much you pay attention to the prevention from Adware and spyware, at times you may find that you have been infected earlier than you thought.
In such case, it is better to install an Adware & Spyware resistance/firewall to your system.

The best Anti-spyware are
1. Norton
2. McAfee
3. TotalAV
4. BitDefender

good Info!! Is very important to prevent spyware and online thieves

What is the best anti-spyware/adware app to use?

IMO, SuperAntiSpyware: http://scforum.info/index.php/topic,116.0.html

Additionally, here you have "The Best AntiSpyWare" topic: http://scforum.info/index.php/topic,102.0.html

And the choice of your anti-spyware and adwares still depend on your preference.

Considering the lengths some companies will go to in order to ensure their adware/spyware cannot be easily removed, the best protection is prevention. Fortunately, preventing adware and spyware is simple enough and won't cost you a dime.

Your first step should be to ensure your system cannot and will not install programs automatically over the Internet or launch them automatically from email. Begin by following the steps outlined in Securing Internet Explorer and the Email Help Center.

Ensure your operating system is fully patched against any known security vulnerabilities. Visit the Microsoft Windows Update site and install any patches marked "Critical". This step should be repeated periodically, at least monthly, to ensure your operating system is fully protected against known exploits.

For example, a common tactic of spyware and adware is to forcibly change your Internet Explorer startup page to their own site. This is often done by exploiting a vulnerability that was first patched by Microsoft in January 2001. Despite the availability of the patch, many users have not updated and continue to be taken by this simple ruse. This is just one of literally hundreds of vulnerabilities in the Windows operating systems that leave your system open to malicious marketeers and virus writers. Keeping your Windows operating system fully patched is the single most important thing you can do to ensure security.

Disable the Windows Messenger Service. The Windows Messenger Service can be exploited and used to dish up unwelcome advertising on unsuspecting users. The service is also victim to a critical exploit that could allow malicious attackers to remotely run code on vulnerable systems. Disabling the service will prevent both the pop-ups and the exploit.

Once you've taken steps to ensure your system cannot automatically download and run malicious code either via the Internet or email, you should see a prompt anytime an application attempts to install itself. Do not click "OK", "Yes", or "Run This Program" to anything unless you fully understand the implications of what it is trying to do.

If you've deliberately downloaded an application, make sure you read and understand the End-User Licensing Agreement before you install it. More often than not, victims of adware and spyware click "yes" or accept the action without reading about its intentions. The following articles discuss some of the tactics employed by two purveyors of adware and spyware. Familiarize yourself with these tactics and apply that knowledge to ferret out other potentially unscrupulous vendors before letting them attach themselves to your system.
Wotch Yourself takes a step through of a privacy statement from Wotch networks and helps identify potential pitfalls.
Beware of Friendly Greetings describes the email tactic and implications of the End User Licensing Agreement from PerMedia sites.
And what to do if you've already become infected with adware or spyware? Follow the tips in Removing Adware & Spyware to rid yourself of these miscreant marketing threats.