I have been looking for free security solutions and thought that it would be a good idea to share and get input from folks here. I found a couple of threads but seems like they have been locked for a few years now so lets collect current and relevant information in the quick summary. Also, I am aware that many of us here get our favorite security solutions for free after rebate but this thread is for totally free software without time limits that is free at least for personal use.
These applications are meant to be your primary security solution. They provide continuous (on access) scanning and protection.
Microsoft Security Essentials - FW Thread. Microsoft's free successor to OneCare.
AVG Free - Antivirus+Antispyware, PC Magazine Review, FW Thread.
avast! Free - Antivirus+Antispyware+Antirootkit, PC Magazine Review.
PC Tools Antivirus Free Edition - Antivirus
Avira AntiVir Personal - Antivirus+Antirootkit
Comodo Internet Security - Antivirus + Firewall - PC Magazine Review, FW Thread.
Ad-Aware Free - Antispyware, FW Thread.
IObit Security 360 - Anti-malware.
Spybot Search & Destroy - Antispyware.
Spyware Doctor Starter Edition - Antispyware.
Windows Defender - Antispyware.
ZoneAlarm Free Firewall - Firewall.
On Demand Scanning and Other Security Tools
These applications are meant to complement your primary security solution. Use them to get a second opinion on the state of your system or to clean up an infected system.
BitDefender Free Tools - Detect+Clean.
Comodo Free Security Softwares.
Google Pack - Includes Spyware Doctor with Anti-Virus. Detect+Clean.
a-squared - Several versions of this anti-malware program are available as a free download. Detect+Clean.
ClamWin - Detect only.
Kaspersky Free Virus Scan - Detect only.
McAfee Free Services - including SiteAdvisor and FreeScan.
Microsoft Malicious Software Removal Tool - Specific threats only. Updated once a month.
Norton Security Scan and Symantec Security Check - Detect only.
Panda Research Free Downloads - See the Free Downloads section in the right column of the page.
Panda Security Free - includes online ActiveScan.
Secunia Personal Software Inspector and Secunia Online Software Inspector - Checks to see if you have applied all updates and patches.
Trend Micro Free Antivirus Tools - including HouseCall and HijackThis.
VirusTotal - Upload a file to get it scanned.
Webroot Spy Sweeper Free Scan - Detect only.
Windows Live OneCare Safety Scanner - Detect only.
Check with your ISP, your employer or your school. Some of them antivirus solutions for free to their subscribers/employees/students. For instance:
McAfee Internet Security for Bank of America customers.
Free trials of security software can be used to scan your computer although most will require you to buy before they fix anything:
CA 90 Day Trial
Norton 90 Day Trial
Windows Live OneCare Trial
Trend Micro 30 Day Free Trial
AVG 30 Day Free Trial
Kaspersky 30 Day Free Trial
Acronis True Image WD Edition - FW Thread. Has significant restrictions on which drives it will work with.
Backup and Recovery Free Edition.
CrashPlan - Supports Linux, Solaris and Mac also.
Easeus Todo Backup.
Macrium Reflect Free Edition for personal use
Seagate DiscWizard - FW Thread
O&O Disk Image Express Edition
Ubuntu One - 2 GB of free online storage for Ubuntu. The sync feature can be used as a simplistic backup, although it will not retain prior versions.
FBackup - Free backup software.
GFI Backup Home Edition.
Other free backup and drive imaging softwares
SyncBack Freeware and other free software.
Uranium Backup Free.
Shadow Explorer - Provides access to previous versions of files saved by Volume Shadow Copy for Vista Home users.
Mozy Online Backup - Free edition is limited to 2 GB.
IDrive Online Backup - Free edition is limited to 2 GB.
MyOtherDrive.com - Free account is limited to 2 GB.
Maintenance and Utilities
Windows Sysinternals - By far the most powerful collection of utilities for Windows. Targeted at system administrators but power users will also find many useful tools here, such as a utility to wipe free disk space for instance. Note that most of these are command line tools however.
Note: In my experience, it is better to avoid registry and drive clutter by minimizing the number of programs that you install, or to do a clean install if you end up with clutter and/or problems. However, if you want, you can try your luck with one of the free registry/drive cleaners listed below.
Advanced SystemCare Free.
Ashampoo WinOptimizer, More Ashampoo Software.
Comodo System Cleaner.
EASEUS Partition Manager Home Edition.
Partition Manager Express and Rescue Kit Express - Create, resize, delete, recover, wipe and manage partitions; some discussion in this FW thread.
Paragon Partition Manager 9.5 Professional: Download 32 bit, Download 64 bit, Register to get serial - FW Thread, older FW thread.
Parted Magic - Partitioning plus utilities. Requires booting from CD image.
Partition Wizard Home Edition.
CCleaner - Registry and driver cleaner.
Eraser - Secure file and drive deletion.
Fresh Diagnose and Fresh UI.
Recuva - File undeletion.
Defraggler - File defragmentation.
McAfee Consumer Product Removal Tool - The helpful guys at McAfee realized that sometimes you may have trouble uninstalling their software.
Microsoft Automated Troubleshooting Services.
Microsoft Fix It Center Online.
Microsoft PowerToys for Windows XP.
Nero Tools & Utilities - includes Nero General Clean Tool. The helpful guys at Nero realized that sometimes you may have trouble removing their software.
PC Tools Desktop Maestro 2.
SeaTools - Hard drive diagnostics for Seagate and Maxtor hard drives.
System Rescue CD.
TuneUp Utilities 2007.
TweakVI for Vista.
VCOM FixIt Utilities 7 Express.
WD Data LifeGuard - Hard drive diagnostics for WD hard drives.
Windows Steady State - Rolls back changes automatically.
Additional Resources: Reviews and Downloads
Hot Deals - Security & Utilities.
V3.co.uk Recommended Downloads
Utilities - Reviews and Price Comparisons from PC Magazine.
Backup Sofware Reviews.
Paragon Software Free Tools.
Techsoup - free software for non-profits.
Previous Paragon Software Giveaways (some may still be available):