Investors wiped almost $13bn from the market value of Computer Associates, one of the world's largest software companies, yesterday after the group issued a profits warning.

Shares in the company opened 40% lower at a 52-week low of $29 (£19). The company warned that its first-quarter revenues would be lower after US stock markets closed on Monday, just before the July 4 holiday. Shares fell as low as $28 yesterday morning from an opening price of $41.

A conference call yesterday designed to explain the company's negative outlook failed to satisfy sceptical analysts yesterday. One fund manager described the call with senior executives of the company as not especially helpful.

Several investment banks, including Goldman Sachs, downgraded the company as a result of the warning that its revenues in June would be about $300m-$350m short of consensus estimates of $1.6bn. Operating profits were also expected to be lower.

Several analysts were angry about the timing of the announcement, which could provoke criticism from the securities and exchange commission. The SEC refused to comment yesterday, while the company said that it had simply made the announcement when it became aware of the shortfall.

Computer Associates was also subject to criticism and shareholder lawsuits in 1998 after the company's decision to grant $1.1bn in stock to its three senior executives.

The company blamed three things for its profits warning on Monday: weak demand for its mainframe software, a failure to integrate acquisitions as quickly as promised and a disappointing performance in Europe.