In response to a concerted effort by cyber criminals to infect the computers of Google users with malware and make them unwitting partners in crime, Google has apparently purged tens of thousands of malicious Web pages from its index.

In a blog post on Monday, Alex Eckelberry, CEO of Sunbelt Software, noted that many search results on Google led to malicious Web pages that expose visitors to exploits that can compromise vulnerable systems.

"We're seeing a large amount of seeded search results which lead to malware sites," said Eckelberry. "These are using common, innocent terms -- one researcher landed on a malware site through searching for alternate firmware for a router."

Sunbelt published a list of search terms that returned malicious pages, the result of search engine optimisation (SEO) campaigns by cyber criminals to get their pages prominently ranked in Google -- Sunbelt refers to this as "SEO poisoning." The list includes hundreds of search strings containing the words "Microsoft Excel," along with a vast number of other popularly technology-oriented terms, products and companies.