I recently installed Clamwin (latest version) on my old computer which is running Windows XP Home Edition. I started a virus scan and it ran for 13 hours and it had not completed which to me seemed extremely excessive. I had used Clamwin before, about 10 years ago, again on an archaic pc but this time running Windows 98. On this machine the scans always completed within the hour and mostly in much shorter times. Is there any logical reason why scans should be not finishing after 13 hours? What am I doing wrong.

Most likely you are doing nothing wrong. Perhaps you also a real-time Av that is interfering with ClamWin during scanning.If so, try whitelisting the ClamWin .exe files located in the ClamWin/bin folder. Remember that Microsoft has dropped support for Windows XP, so there may be something in the ClamWin source code that is responsible for your problem. It is getting very hard for the ClamWin developers to support the Windows legacy OS.

You do not have to scan your entire computer. Malware most likely will infect the user\appdata folders, the Windows\system 32 folder, and the Windows\SysWOW64 folder (in computers after Windows XP models).

You also do not have to scan every file on your conmputer. You will scan more efficiently if you just scan about 40 to 50 extensions that malware likes to hide in. Here is my extensions to scan list (show as *.extension in the ClamWin Tools, Perferences, Filters, Patterns configuration option) (this is just my list--feel free to develop your own):
bat, cab, chm, cla, class, cmd, com, cpl, dll, doc, docx, exe, htm, html, jar, jpe, jpeg, jpg, js, jse, lnk, msi, ocx, pdf, pif, ps1, rar, rtf, scr, sys, txt, vbs, xls, xlsx, and zip.

Thanks for using ClamWin!

Regards,