St Bernard already offers email security in software and appliances. The acquisition brings it into competition with the likes of Postini and MessageLabs.

Singlefin’s three-year-old hosted service is said to filter five billion messages a day, mainly through a white-label partnership with the United Online Inc, a US consumer ISP.

The deal is for an undisclosed amount. St Bernard, which went public on the Over The Counter board with a recent reverse acquisition, had only about $22m in current assets on its June 30 balance sheet.