Why do you think that the link wasn't prefetched?
Because WebShield should block the file BEFORE it is even saved into the disk.
Tech - I run the Home version, not the Pro version, so I don't have the option to run a boot time scan.
Home version has boot time scanning too.
If you can schedule one from the Home version please advise how. I don't see it in the avast! documentation.
Start avast! > Right click the skin > Schedule a boot-time scanning.
Doing so displays a dialog allowing you to schedule virus scanning.
Check Archives, if you want scan all the archives.
Specify whether all the disks or just a specific folder should be scanned.
Select Advanced options for scheduling details.
Select how to automatically process infected files.
Choose how to automatically process infected system files.
Click the Schedule button to confirm the settings.