Hack attacks targeting US utilities have almost doubled this year, a security firm warned today.

Managed security services company SecureWorks estimated that it blocked an average of 49 attacks per utility client every day from January to April 2007. But this increased to an average of 93 per day between May and September.

"When researching these new statistics, we found that web browser attacks represented a large number of the attacks attempted against our clients, including our utility customers," said Wayne Haber, director of development at SecureWorks.

"In 2007, we blocked significantly more browser attacks for our clients then we did during the pervious year, as many of the top Trojans are using websites and email links as infection vectors.

Some of the most prominent malware using these tactics include the Gozi, Prg, Storm and BBB/IRS Trojans, according to SecureWorks.

"Unfortunately, there are companies that do not employ an intrusion prevention solution and depend solely on antivirus software to protect them," Haber added.

Utility providers can protect themselves and their employees more adequately by implementing strong internet usage policies for employees, and checking for software updates frequently.

Companies should also educate employees on the latest social engineering tactics so that they are aware of the dangers and how to avoid them.

SecureWorks 100 US utility providers as clients.