Install avast, you will be asked at some point to do a boot-time scan when the system reboots, answer yes. This will do a scan before windows starts, so if you have picked up anything hopefully it should be detected before it can start.
You should also ensure that you have a firewall installed, essential and preferably one that has outbound protection. Whilst the windows XP firewall is usually good at keeping your ports stealthed (hidden) it provides no outbound protection and you should consider a third party firewall.
Any malware that manages to get past your defences will have free reign to connect to the internet to either download more of the same, pass your personal data (sensitive or otherwise, user names, passwords, keylogger retrieved data, etc.) or open a backdoor to your computer, so outbound protection is essential.
- There are many freeware firewalls such as, Comodo, PCTools Firewall Plus, Jetico, etc. - Zone Alarm free works fine with avast and has a reasonably friendly user interface, however, the free version is becoming bloated with trial ware and is also crippled as far as outbound protection goes In the Program Control, configuration area, the slider will only goes as far as Medium protection, if you want more you have to buy the Pro version.
See A Forum discussion on free firewalls
http://forum.avast.com/index.php?topic=30808.0See
http://www.matousec.com/projects/firewall-challenge/results.php.
It would be worthwhile running some other tools (and keep them installed as back-up scanners to avast, something that you can update and run once a week):
If you haven't already got this software (freeware), download, install, update and run it, preferably in safe mode (for the first scan) and report the findings (it should product a log file).
1.
SUPERantispyware On-Demand only in free version.
2. MalwareBytes Anti-Malware freeware 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.
