During March, MessageLabs intercepted 716 e-mail messages that were part of 249 targeted attacks aimed at 216 of its customers, the Gloucester, England-based provider of hosted e-mail filtering services said in a research report. Of the attacks, almost 200 consisted of a single malicious e-mail designed to infiltrate an organization, MessageLabs said.

“These numbers represent a significant increase when compared to the same period last year when attack rates reached one or two per day,” MessageLabs said.

Security experts have said that limited-scale attacks are the most dangerous. Widespread worms, viruses or Trojan horses sent to millions of mailboxes are typically not a grave concern because they can be blocked. But targeted Trojan horses, especially those aimed at specific businesses, have become nightmares as they can fly under the radar.

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