> In checking the error logs, I found there are some 
> files marked being purged by winhttrack; however, 
the 
> files are still useful to me. Under what 
circumstance 
> would httrack PURGE files? and is there any ways to 
> prevent it from happening?
To prevent that: activate the option 'do not purge old 
file'

Files are being purged when the engine is updating a 
mirror, and does not detect files that are locally 
present. This is the case, for example, when you 
remove a link in the remote site. In this case, the 
engine will wipe the local file, to attempt to match 
the remote structure. Files are also being purged 
locally when you change specific options (like 
filters) and re-run the mirror: updating/continuing a 
website using a new filter '-*.gif' will force the 
engine to erase all local gif files!