Some Viruses or Worms can Reinfect Your Computer. Why?
This might happen for example if the malware
(worm/trojan/backdoor etc.) uses Windows network and drive shares that
are behind weak password to spread. An example of this is the Randex worm:
Change all passwords in your computer to good
ones, and remove unneeded user accounts. In this way you can prevent
reinfection. Other option is to install a firewall (included for
example in F-Secure Internet Security and F-Secure Anti-Virus Client
Security) and block Windows network shares with it.
If the virus warning keeps reappearing every time
you start a browser, change the home page to a different page. This is
the case especially if the full path to the infected files includes text "Temporary
internet files" or for example "Cache". The warning comes then probably
from the HTML document that contains malicious code segments. An
example of this is warning is the Iframe exploit: