With shared hosting, your site can fall victim to malware, viruses or intrusion hacks when other sites on the same server have poor security measures. However, with a dedicated server, the entire server is only available to you, so the security issues of other sites won't affect yours. The only people who would have access to your site other than yourself (and your IT team) are the staff of the site which manages your hosting. And, these people are very invested in keeping you safe.