Meanwhile, yields on 10-year Spanish government bonds surged to 6.958%, according to electronic trading platform Tradeweb, after Moody's Investors Service downgraded Spain's debt three notches to the brink of junk territory late Wednesday.

WSJ: Blue Chips Jump 156 Points

Most of the online firms are now rapidly transforming themselves from low-cost trade-executors into electronic financial-service companies offering a full range of retail products, from share-trading to insurance.

ECONOMIST: The real virtual business