The frequency of infections from Web pages has climbed dramatically in the past year, according to antivirus firm Sophos. In the first quarter of 2008, the company identified about 15,000 infected Web pages per day, compared to about 5,000 the same period a year before. In addition, a growing percentage of the sites—currently about 79 percent—from which users got virus infections are legitimate, as opposed to being sites that exist mainly for malware distribution.