With markets immediately comparing Adecco's scantily-worded disclosure of bookkeeping problems to a wave of accounting scandals that has rocked the business world and sent investors scurrying, the firm's stock plunged as much as 48 percent.
The loss wiped out last year's 47 percent share price gain made on the back of hopes that a global economic recovery would benefit the firm's sprawling temp business.
Adecco refused to disclose details of the irregularities it had found in an internal review, leaving dealers to worry the issue could balloon into an accounting scandal similar to those at Enron, Ahold and Parmalat, where billion-dollar frauds have triggered criminal probes.
Adecco said legal reasons prevented it from saying more than was in its initial 14-line statement on a delay in the release of 2003 earnings, but some analysts said the issues might be connected to the March 2000 acquisition of US jobs firm Olsten.
Formed from the merger of France's ECCO and Swiss Adia in 1996, Adecco makes about a quarter of its revenues in the United States. Adecco Staffing represented some 90 percent of group revenue of some 25 billion Swiss francs ($20.6 billion) in 2002.