MOUNTAIN VIEW, California: Now the world knows it's a recession. Lehman Brothers, AIG, General Motors – kid's stuff! But when the seemingly impregnable Google sees its stock go south to its lowest level since late 2005, it's time to head for the hills.

The shares fell by $20.46 (6.6%) Wednesday to $291.00, more than halving its value in the year to date, reports USA Today.

The state of the planet's economy has eroded many companies' ad budgets, which in turn impacts on paid search ads – Google's primary source of income.

Citigroup analyst Mark Mahaney cut Google's Q4 earnings and net revenue forecasts by 3%, to $5.03 a share and $4.16 billion, respectively. And for fast-looming 2009, he lowered his earnings and net revenue forecasts by 5%, to $21.18 a share (equating to $17.46bn).

Another key factor is Google's cost-per-click charging method. Predicts Collins Stewart analyst Sandeep Aggarwal for Q4 and 2009: "We believe that the high c-p-c inflation Google has been experiencing for the past six quarters is not sustainable and will pressure core search growth."

Data sourced from USA Today / Reuters; additional content by WARC staff