An eCommerce websites must be hosted under the isolated and more secure environment like either VPS Hosting or dedicated server. The web shops are never recommended to be hosted under shared environment because you will be sharing the server resources with 100s of other websites.
While you run a eCommerce website, you are storing the most critical data such CC details of customers, personnel details of customer, billing addresses etc. You never know what website's going to be compromised and that might affect your website as well. So, hosting web shops in shared host is the major security risk.
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