According to BBC News, One of the worst hit was Ciao.co.uk, a Microsoft-owned company that had been leading an EU competition case against Google -- claims that Google is involved in rigging searches following the recent Panda update which was designed to "reduce rankings for low-quality sites".
Ciao.co.uk's web visibility fell by 94% according to analysis by Searchmetrics. It was also involved in initiating an EU investigation into Google in November 2010.
Parent company, Microsoft, claims that Google has used its dominant position to limit rivals' products.
Google's head of search evaluation, Scott Huffman, said it was "almost absurd" to suggest that the results were rigged.
The company regularly changes the algorithms that determine what users see when they search.
Such updates are often done to weed out "content farms" - websites that copy material from other sites in order to get hits.
Where a keyword search may previously have returned their site on Google's first page, afterwards it may be relegated to further down the rankings.
"A 94% drop is astronomical," said Sanjay Shelat, a search engine optimisation (SEO) specialist at Edit Optimisation.
"It's very unusual to take such a hit in an update. That is enough to put a company under."