The trend for cybercriminals to shift focus from larger organisations to SMEs as weaker links in the supply chain appears to be accelerating, according to the latest monthly Symantec Intelligence Report.

Almost 36 percent of targeted attacks were now aimed at SMEs, Symantec said, with the company blocking an average of 151 per day during May and June.

Symanted defines an SME as being an organisation with fewer than 250 employees (some vendors users larger numbers which can make comparisons difficult), and said that as recently as December 2011 the sector accounted for only 18 percent of targeted intrusions.

That SMEs are moving closer to centre stage is not in dispute but what matters more perhaps is why this is happening.

Larger organisations are better defended than smaller ones, but in Symantec's analysis there could be more method than simple effort and convenience.

“There appears to be a direct correlation between the rise in attacks against smaller businesses and a drop in attacks against larger ones. It almost seems attackers are diverting their resources directly from the one group to the other,” said Symantec's security intelligence manager Paul Wood.

“It may be that your company is not the primary target, but an attacker may use your organisation as a stepping-stone to attack another company,” he warned. “You do not want your business to be the weakest link in the supply chain.”

The risk of being a target for all organisations depends to some extent on sector, with the defence industry and public sector an obvious top catch for cybercriminals. Pharmaceutical and manufacturing are next on the list.

“It is important to remember that although on the increase, targeted attacks are still very rare,” said Wood. Despite this comforting thought, targeted attacks are also likely to be more serious when they do occur, he might have added.