Google has responded on the security problems experienced by Adword and Google Search Engine users:

Google is committed to ensuring the safety and security of our users and our advertisers. We actively work to detect and remove sites that serve malware in both our ad network and in our search results. We have manual and automated processes in place to detect and enforce these policies, and products such as Google Toolbar that actively seek out and alert users when they access malicious or suspicious sites. We feel a responsibility to protect the security and safety of our users and advertisers, and recognize that secure products are instrumental in maintaining your trust.

And advise us to update our anti-virus softwares:

We strongly encourage all of our users and advertisers to keep up-to-date antivirus protection on their computers and regularly run system scans. As a general rule of thumb, individuals should also take care to create complex passwords, change them frequently, and only use them on known or trusted (non-public) computers. Antivirus software (such as Norton Security Scan and Spyware Doctor) and instructions for use are available for free as part of Google Pack.

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