Introduction: The growth of internet health information with unclear quality endangers Users' health and lives. The necessity of evaluating intrenet sources including web has been proven, in many studies. Therefore, applicable solutions for evaluating internet information in web are suggested, one of which is the systematic rating of web information using a criteria and based on different aspects of technical characteristics, etc. this study was done to rate websites providing information on viral infectious diseases, in regard to updating, Silberg score, information comprehensiveness and accuracy based on Silberg and WHO criteria.

Methods: Sixty three viral infectious websites were searched using a key phrase "viral infectious diseases" in search engines: Google and Askjeeves. Websites characteristics were obtained by "website characteristics evaluation checklist" each of which was given a score from 9 according to Silberg criteria. Viral infectious information on hepatitis B was corresponded to "WHO standard checklist for hepatitis B treatment" adapted from a document by World Health Organization as WHO criteria and 20 websites including hepatitis B treatment information were given scores on comprehensiveness and accuracy codes.

Findings: Rating viral infectious websites based on the latest updating based on, Silberg score, scores on comprehensiveness and accuracy code showed that updating time for most websites was December 2003 (57.14%). Also, about 12.69% of websites obtained the highest Silberg score as 9. Regarding Silberg criteria, most websites did not notify their cited references (63.49%) and the original date (58.73%). The highest score on comprehensiveness was 46 out of 223- WHO criteria checklist- (20.62%) of total point) that belonged to only one website, and 20% of websites obtained only one score. Most websites (35%) obtained score between 2 - 6. Also, regarding accuracy code, about 85% of websites obtained accuracy code 1 indicating the accuracy of information on hepatitis B treatment. About 15% of websites also obtained code 1 indicating at least one error in their statement Most sources included health subject index (65.70%), link to other internet sources (61.9%) and selected medical health news (60.31%).

Conclusion:The current ratings show that the status of viral infectious information is weak in upgrading information, accuracy, comprehensiveness and meeting Silberg criteria and the users are recommended to be cautious and aware of evaluation means when using website providing health information, particularly on viral- infectious diseases.