Computers running Windows seem to have virus and spyware problems quite often. When fixing other peoples computers, I have found these free options to be very useful.
Free Windows Anti Virus Software
ClamWin Free Antivirus
ClamWin is a Free Antivirus program for Microsoft Windows 7 / Vista / XP / Me / 2000 / 98 and Windows Server 2008 and 2003.
avast! Free Antivirus
Free Anti-Adware / Anti-Spyware Information
Some of this Windows software is offered as a free version, with an option to upgrade. Generally, the free version is enough to clean any problems, but has to be run manually.
Ad-Aware – check for updates, and run occasionally
Spy Bot Search and Destroy
Malwarebyes Anti-Malware is often the best tool to remove fake anti-virus software.
Super Anti Spyware
Super Anti Spyware: Remove spyware, NOT just the easy ones!
More adware stuff here: http://www.cexx.org
I have found this site to be an excellent resource, with information on computer security: http://www.selectrealsecurity.com
Behavioral Advertising Opt Out
Have you noticed that certain types of ads appear after you visited a particular website? That is called Behavioral Advertising, and is usually done by storing cookies on your computer.
The Network Advertising Initiative has to offer the ability to opt-out. Go to their website, and select opt out.
You may be surprised at how many active cookies you have.
Another place to opt out:
I am not a big fan of the opt-out idea, as it has to potential to give information to precisely the people you don't want to give it to. It's like calling a telemarketing company and saying, "Here's my phone number, please don't call me." The scammers can still use the do not call list to pretend they are a charity. I would rather not be on a list. By the way, there is an article on how to defeat telemarketers on the systemnotes.org blog.
Web Browser Security
Browsers also have options to clear the cache, and history, but you may not want to clear all history and cookies, since they can make browsing your favorites sites easier. You may have to opt out again after clearing cookies.
Check for the latest Add-ons or Plugins for your browser. For example, in Firefox, select Add-ons, and search for some of these terms: "Do Not Track", privacy, block, security, ad, virus, etc. There are lots of good options available.
People generally think of viruses when a computer starts acting strange, or starts running slower, but there are all kinds of bad programs known as malware. These include worms, trojans, rootkits, rouges, dialers, spyware, viruses, etc. It may be useful to search the internet on those terms when attempting to clean a computer. Your computer may be used to store someone else's illegally copied files.
There are plenty of other software options, but many do not offer a fully functional free version. Free trials are not as good, in my opinion. Some of the major anti-virus publishers offer free scanning tools as well, so it can be helpful to check their sites for the latest offers.
Remember, when all else fails, you can always re-install Windows. Or better yet, upgrade to Linux :-).
Sysadmin Notes: Systems Administrators are usually familiar with resources for securing systems and networks they are responsible for, but software is updated frequently, so it is good to have sources to check for updates. One of my favorite sources for Open Source software has been sourceforge.net, but use caution, since anyone can upload software.
Security Software Resources
http://insecure.org - nmap, and network security
Be careful with this site, as malware seems to show up occasionally:
I'm not sure about the next one, since McAfee SiteAdvisor gave a warning that it may be a dangerous site: YAC - Yet Another Cleaner http://www.yac.mx
"YAC: The World's Fastest & Lightest PC Cleaner
Fast, Easy to use PC cleaning software. Clean junk files, privacy files, potential adware, and malicious plugins."