Can quarantined viruses harm a PC eventually?

No, a virus can't harm your computer while it is in quarantine. Some AVs "mangle" them, but ClamWin just puts an "infected" on the end of the filename, so it can't be activated. You can remove a virus manually from the quarantine folder. You can restore a file from quarantine by running the Clam QRestore program.

Regards,

What if I uninstall the antivirus, will it activate the quarantined virus or not? And what is the use of this quarantine, if the antivirus has discovered a potentially dangerous program (example trojan) why not delete it immediately? Any thoughts is appreciated. Thanks.

Uninstalling ClamWin will not activate the virus. All ClamWin folders, including quarantine will be delete upon installation.

Not all detections of a virus are are correct. Sometimes there can be "false positive" detections. If ClamWin detects a virus in a file that is not really infected and removes the file, you could lose some important information or even lose access to an important Windows file if the file is not digitally signed by Microsoft. As long as a file is still in quarantine, you can recover it by using the QRestore.exe program, which will let you put the file back where it belongs.

You can verify files by uploading them to Jotti or Virus Total.

Regards,