Repeated "malicious URL blocked" popup

[chipsahoyavast]

Hi. I'm new to this forum so if this is in the wrong place, apologies in advance! Beginning last night I've been getting the same popup intermittently, not always when I've initially clicked on a site.  Sometimes it will pop up even if I've been at an all-text site (no pictures or graphics) for quite a while without going to any other sites. I took a screen grab and will try to attach it. In case it doesn't show up, it says "Malicious URL Blocked" and also says:

Object: asia-news100.com/cfg/passw.plug
Infection: URL:Mal
Action: Blocked
Process: C:\WINDOWS\system32\svchost.exe

I'm on Windows XP and version of free Avast is 5.0.677 (last notification of automatic update was just a few hours ago, and does not seem to have affected these popups).

When this first started last night I had not downloaded anything new and browsing history had not deviated from usual. I realize there could be a new infection on one of the usual sites I visit but am wondering if this might be a false-positive which I have seen reference to before, and how do you tell if it is? Is there something I should do within my Avast program itself to have it manually check for a problem? Thanks for any help and again apologies if I'm posting in the wrong place!

[YoKenny]

XP SP level?

Current avast! is v6.0.1000

[kubecj]

This is Carberp malware trying to get additional plugins.

[chipsahoyavast]

Thanks for the fast replies!

Ok, I feel very sheepish - I manually updated to 6.0 when I saw YoKenny's msg a few minutes ago... but now I have what might be a dumb question, please bear with me - why did I have to manually "update" to bring me current to 6.0 if I have been periodically getting the green popup/audible notice "virus database has been updated" (most recently earlier today)?  I get that it is updated virus definitions (not sure I'm using right term there) when it says that specific thing but does it NOT automatically update to the new "version" of the program itself? Not sure if there's some setting I have missed to make it do that but in any case thanks for prompting me and for not laughing at the newbie! at least not out loud!

Kubecj - I don't know what Carberp is - now that I've got my Avast current should I continue to have a problem? Thanks again.

[DavidR]

Effectively you have a hidden or undetected malware (trojan downloader) on your system.

Try scheduling an avast boot-time scan.

If you haven't already got this software (freeware), download, install, update and run it and report the findings (it should product a log file).

• 1.  MalwareBytes Anti-Malware (MBAM), On-Demand only in free version http://download.bleepingcomputer.com/malwarebytes/mbam-setup.exe, right click on the link and select Save As or Save File (As depending on your browser), save it to a location where you can find it easily later.
• 2. SUPERantispyware (SAS). On-Demand only in free version.

Don't worry about reported tracking cookies they are a minor issue and not one of security, allow SAS to deal with them though. - See http://en.wikipedia.org/wiki/HTTP_cookie.
Also available, a portable version of SAS, http://www.superantispyware.com/portablescanner.html, no installation required.