I guess you intentionally downloaded or otherwise installed
Putty?
There is a chance it's a FP.
Please stop any programs that may be using it, and exit out of it (Putty) if running, then move it to the chest under "user files" or allow Avast to quarantine it. check that the chest maximum size limit is not set to be too low for it to be moved there.
Right click on the file, and send it to Alwil under the report false positive option. If it is a false positive, Alwil are fairly quick about correcting such detections. Re-scan it periodically from the chest and when/if it scans clear, it can be restored.
Get a second opinion. (This is a good demand scanner to have, anyway.)
Download and install the free version of
MBAM. Update it and right-click the file for a context-menu scan with MBAM.
This will give an indication.