Washington - Knight Capital Group said on Thursday that a software glitch which rattled the New York Stock Exchange will cost the firm around $440 million.

The mishap, which caused the firm to unintentionally buy and sell millions of shares in over 100 companies, roiled markets at the opening of trade on Wednesday.

Unwinding the trades will cost the firm close to half a billion dollars and has “severely impacted” its capital base, Knight said.

Knight's stock was down 49.35 percent at the open on Thursday.

On its website the firm boasts it executes an average of 218.8 million share trades per day using sophisticated trading technology. - Sapa-AFP