The standard response should be “make sure your virus definition files are up-to-date and scan your system”. I imagine you tried that.
Yes, something on the harddisk that is not being detected as malicious. To narrow down what it may be, try Trend Micro’s System Information Collector (SIC) utility.
Here’s an easy way to find suspicious files that you can give your antivirus vendor. You can detect that which they don’t detect. Use Trend Micro’s System Information Collector utility. See “<a href=”http://esupport.trendmicro.com/Pages/Collecting-malware-samples-and-logs-using-the-System-Information-Colle.aspx”>Collecting malware samples and logs using the System Information Collector (SIC)</a>” for download and usage instructions. (This particular page does not indicate that Windows Vista among the supported Operating Systems, although other references indicate that it is supported.) With this utility you will create a log file of system information and create a ZIP archive of suspicious files. Review the log file if you like, that’s optional. The important next step is to get the files that were archived to your antivirus vendor for review. The password for the ZIP file is “virus” (without the quotes).
Note that SIC doesn’t remove the suspicious file, just helps you find it. You can use virustotal.com to confirm that yes, indeed, you have come across a file that your antivirus software is not detecting.
Removal will depend upon what is detected.
Even if you will delete those virus programs infinite times, they would keep on appearing. Your computer or other files and folders from your computer system might be infected with that certain virus. You can only solve the virus problem in your computer system by installing the latest and update antivirus software and perform a full system scan.
Yes, most viruses and malicious software hide itself as a system file so that the user cannot delete it totally. Remember that you cannot delete a system file, all you can do is to use an effective and updated antivirus software to scan these malicious programs hiding somewhere else in your system.