How to Tell if a Computer Is Taken Over by Botnet


Botnets are a major network security threat to home users and system administrators alike. These networks infect and assimilate personal computers using computer viruses, then use the infected computers to spread the virus further and expand the botnet. Detecting a botnet on your computer is difficult, as there may be no evidence that it is there, save that your computer may start running more slowly than before. The only way to definitively detect a botnet is to either scan your hard drive for installed malware or to monitor your computer for unauthorized activity.

  • Monitor your network activity. Botnets most often use mail programs and ports reserved for email activity to propagate themselves to other computers. Port 25 is the most common port used for this purpose. Click the "Start" menu, then "Command Prompt."

  • Type "netstat -an" to list the active ports. Port 25, if it is active, is listed in the format "" under the "Local Address" listing. If this port is active and listening, there is a chance that your computer has been infected.

  • Run a malware scanner. Botnets usually use trojans, spyware and other common forms of malware that can be picked up by a malware scan. Spybot, for example, is a free malware scanner that focuses on spyware, and Malwarebytes and Avast! offer similar solutions for your network. Download one of these products (see Resources), then run your chosen application and allow it to delete any viruses it detects.

  • Download and install a botnet scanner, such as RUBotted and BotHunter, to scan specifically for botnet activity (see Resources).

Tips & Warnings

  • Always keep your virus scanner updated.
  • Never install software that does not come from a reliable provider. Check the URL before downloading.


  • Photo Credit Joe Raedle/Getty Images News/Getty Images
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