McAfee will acquire ScanAlert, a Web application security vendor, for $51 million, the companies announced on Tuesday.

ScanAlert, which was founded in 2001, runs a paid service that scans websites daily looking for security vulnerabilities and checks if e-commerce applications have up-to-date patches.

McAfee said the business will be integrated into its Web Security Group, which develops McAfee's SiteAdvisor service. SiteAdvisor scans websites and scores them according to their risk, taking into account for example whether malicious software is hosted on the site. Consumers can download the SiteAdvisor toolbar that displays that ranking in a group of search results.

Sites using ScanAlert's service display a logo that says "Hacker Safe," which also appears on product listings on Web sites such as Yahoo's shopping channel and The service is aimed at increasing consumer confidence with e-commerce transactions, which have seen a rising level of fraud.

SiteAdvisor, which is a free download for Internet Explorer and Firefox but also offers a paid version with more features, will eventually show the "Hacker Safe" logo in search results, McAfee said.

ScanAlert said it has 8,000 customers that have more than 75,000 websites. Its clients include clothing retailer Guess, Toshiba and Warner Brothers. ScanAlert expects its booking revenue to be in the range of $15 million to $20 million this year.

Earlier this month, McAfee splashed out $350 million for SafeBoot, a Dutch company specialising in encryption and access control.