First, please do not follow the advice in the above post.
1) First, we recoomend you do NOT use Spybot - it is old school. For malware we recommend MalwareBytes or SuperAntispyware (regardless of what the above post may indicate, the term "malware" includes spyware ). You should also use SpywareBlaster
2) There are plenty of threads on this forum asking the exact same question. A search on the forum will answer your questions. However, when choosing an antivirus there are plenty of good choices. My favorite is Kaspersky, but it's not free. Among the better free choices are Avira and Avast
3) Most important is "smart computing" - know where you go on the web, don't open email attachments unless you know the source, etc.
4) Last, whenever possible software should be downloaded from the authors' sites, not from third party sites as indicated in the above post.