Note:  No anti-spyware software will catch everything.  It is good to series of other anti-virus software peroiodicly, right now if you are suspcious quortety if you are a heavy user of the internet, anually otherwise.

Windows (Microsoft) Defender comes installed on Vista, Windows 7, and Windows 8.1 and Windows 10. It can be installed in Windows XP system. In Windows prior to Windows 10 it was an incomplete anti-virus program and should be replaced with something better such as something from the list below.  It also should not be running in conjunction with any other security software.  Some anti-virus software such as Microsoft Security Essentials and Defeneder automatically turn it off when other anti-virus softeare is  install.  It can not be uninstalled but it can be turned off.   If you remove your other anti-virus software and want to return toe Defender, I am not certain whether it gets turned on or not.  You would need to look into this.  The windows 10 version will as you to run Windows Defender Offline if it encounters big enough problems.  When it runs it, it will start it up as part of turning doing a restart.

Other free Anti-Virus programs

Your internet service provider may have a free version of one of the good paid ones you can download on all of your computers on the network going through them.  I have Comcast and they have a free copy of the Norton Security Suite.

Consumer reports May 2014 recommendations (and score) Avast Free Antivirus (57), Avira Free Antivirus (53), AVG Antivirus Free but no longer easily free (51), Microsoft Security Essentials (38)

Avira Free anti-Malware, top rated by CU in their June 2010 Issue.  Note, they will try to sell you the paid one so be careful.

AVG Anti Virus (Anti-Malware)  from  http://free.grisoft.com is no longer free unless you install the trial version then go through some complicated hoops when the trial expires.

There may be a free anti-virus program with your internet service provider.  In my area Comcast offers Norton.

K9 Web Protection  Free   parental control software,  PC Magazine April 2010 recommendation.

Pay Anti-Virus programs

Consumer reports latest issue as of Oct. 2018 recommendations (and score and price) Bit defender (80) $40, Kaspersky Internet Security 2018 (76) other versions lower, McAfee (52) $55, others such as ESET, G Data, F-Secure, Avira Internet Security Suite, Avast Internet Security, BullGuard, Trend Micro, AVG Internet Security, Norton Internet Security, Microsoft Windows 8,10 Defender Free, and Panda not reveiewed

The biggest news from this list is that the biggest players, Norton and McAfee are not that good with half of the free programs doing better

Kaspersky Internet Security has been getting a lot of good reviews lately.  It is $49.95 for 3 devices at the Best Buy web site (where you can down load it) and came free with a computer I bought at Best Buy.  It is $59.95 for a multi device license directly from Kaspersky. There is apparently no single device offered by anyone.  There is also a free 30 day trial available directly from Kaspersky.  This is program my current favorite.  As of 5/24/15 when you get  the free trial and do not sign up right away they start lowering the price of their 5 device package down to $44.97 when you are at the last day.  When I did a full scan on my system it took about 8 hours and looked at 5,911,993 files.  A couple of side benefits is it will help you update other software when updates are available and it will worn you if one of your hard disks is starting to go.

Spyware Doctor with antiVirus   $39.95 direct,  PC magazine first choice for anti-spyware suite in May 2010  Also good for malware removal. 

Eset Node 32  Anti-virus $39.99/Yr with 30 day free trial.  http://www.eset.com/products/nod32.php This is a particularly good program for computers that are being bogged down by their current anti-virus software.  Lags behind in all other categories.

Webroot AntiVirus with AntiSpyware;  Top rated basic anti-spyware program.  $38.99 for up to 3 devices.

Norton Security deluxe,  It is free with some internet access firms such as Comcast. otherwise $49.99 for up to 5 devices.

McAfee Total Protection, $44.99 for up to 3 devices.

Zone Alarm Pro will run in the safe mode with networking but not the basic safe mode.

F-Secure from a company in Helsinki Finland.  They have a 30 day free trial offer and 2 online tools you can use for free. One is a general health check of your computer and the other scans for viruses. I tried the 2 free tools and they worked well. They were mentioned as being good at getting rid of ransomware in a Dec 2012 New York Times article.

Sophos is an English company They have a free trial and some free tools including one to remove viruses and one to scan your network for problems. They were mentioned as being good at getting rid of ransomware in a Dec 2012 New York Times article.  You have to set up a free account with password, then request the free program then use the user name and password supplied with the free program to get the latest threat data. If you make it successfully through that labyrinth then it will want to know your username, password, and domain name for the account that has administrator privileges.  Since my home system does not even have a password, I was dead in the water so was not able to evaluate this product.

Parental Control Programs

Net Nanny ($39.99) or Net Nanny Home Suite  ($49.99) are highly rated programs to place parental controls on a computer.     http://www.netnanny.com/

See K9 Web Protection above for a free parental control program, not as good as Net Nanny but cheaper.  One weakness of this program is it has no Chatware controls for sites like Facebook

There is also some capability built into windows but I have not explored that.

Web Sites

Sucuri Site Check offers a free check of your web site or anybody else's. On my site it found no problems but recommended I install a web site firewall.  They have ones available starting at $9.99/Mo. I ran the same check on a much bigger commercial site, www.ghc.org and got the same report.  I opted to pass at this time.  I  do have SiteLock Secure Plus through my web hosting company, Fatcow, at a cost of $49.95/year.  It has caught problems twice or once every couple of years. One was quite serious.  I was on the road at  the time and had to edit my web site from my smart phone.  A first for me.