I can understand your reluctance to upgrade your system, but that in itself makes it hard to support your system setup.

Avast 5 came out over two years ago and avast 4.8 is on life support right now.

The real problem is that it is over two years since I last used avast 4.8 and much of what I knew about it is forgotten, so it is very hard to support very old versions.

I honestly can’t recall how good the 4.8 anti-rootkit function was or even if it had one, I have managed to find an old image of a rootkit detection in 4.8

The one incorporated in avast5 onwards was much better and crucially continued development were the the one in 4.8 is effectively frozen in time.

However, that said it is strange to get an alert on explorer.exe as a potential rootkit. So I would suggest that you check the option to ‘Submit the file’ for further analysis.

I would also suggest trying a stand alone anti-rootkit application also, but again finding one that supports XP SP1 might be an issue.