Online Security Checks:
Symantec - Security Check
Sygate - Sygate Online Services
McAfee FreeScan - Free Scan
Gibson Research Corporation - Shields UP
Trend Micro's - Trend Micro™ HouseCall
F-Secure - F-Secure Health Check
EMSI Software - a-squared Web Malware Scanner
Planet Security - Probe your ports / check your firewall
PC Pitstop - Multiple Checks
Scanit - Browser's Security Test (Attempts to crash your browser be careful)
MyServer.org - Port Scan Your Computer, Has Custom port scan option

Feel free to Add Your own as well.

[Edited to add more resources]

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Your Friendly Neighborhood Admin.

yes the links and viruses has to be detected and one has to be careful with the viruses and the hackers, without it you cannot be go smoothly and has to face the new problems again and again.

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Pontiac Grand Safari Parts