...because it's Free, it's pretty effective (nothing is 100% effective), although I've never used it in anything other than english, it appears to it supports over 30 languages (including spanish).
The default mode is very simple and straightforward. Have it scan for problems and use the "imunization" tool.
The advance mode is pretty good at adding more protection options, but doesn't offer a whole lot of help in explaining what the various tools in advanced mode do. I've been slowly tinkering with the advance options to learn what they do, but if you're not sure you should probably leave advance mode alone or get help in using it.
Spybot Search and Destroy is free (although they encourage donations) and you can download it off a number of sites, including the CNET Download center.
Go download it, have it check for updates, then run the scan and imunization.
I wouldn't use it as my only anti-virus/anti-spyware, but it's a lot better than nothing and works well in combination with other similar programs.
Hope that helps.
I downloaded the free ZoneAlarm yesterday. Today it scanned and showed me two new spyware but wouldn't remove them without me purchasing one of their products. I have found the same for a couple of other products that are suppose to be free. Gee, I appreciate the free scan but I am looking for something that will work to remove the junk.
Also someone knows of a good Spanish version that I can put on my computer in S.A. for my non-English speaking kids? I have ZoneAlarm(free), Spy Sweeper (30 free), B-Safe Online (AV), but it is all too complex for someone who doesn't understand English.