How does search engine malware spread?

Expert Richard Brain explains how malware can take advantage of Web crawlers and spread malicious code to a number of vulnerable websites.

How have search engines been manipulated by attackers to spread malicious code, and what are best practices to avoid search engine malware?
Yes, search engines or 'Web crawlers' have been used to indirectly attack other websites. It's actually quite an old idea which was confirmed still to function fairly recently, when Google was used to carry out RFI attacks and hack into other sites.

Search engines 'crawl' domains by looking for links to other pages or sites. The search engine then opens the link of a website page to find further links.

Search engine attacks have been demonstrated where a malicious link is added to a page, which consists of an attack, or multiple attacks, on other websites; they are then executed when the search engine opens the link. If the attack is successful, visitors to the now infected website would be at risk, and if the malware is sufficiently clever, it would add new links to attack further websites and spread the infection.

I guess such malware would these days be classified as a search engine piggyback virus, as it would not directly perform the attack(s) itself.

As an end user, best practices for avoiding search engine malware are to:

  • Make sure your computer is fully patched and is running the latest antimalware packages.
  • Try to only "visit" high-profile secure sites
  • Disable JavaScript execution on your Web browser if the site is unfamiliar.

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