Need help for zencart website that is maliciously redirected

We have a site [login to view URL] Recently some customers called the said that when they entered our url in the browser, they were taken to another website: [login to view URL] However, we tried a lots of times on different computers with various IPs, we could not find any problem. But when we check our website on [login to view URL], we found the website was indeed 302 redirected to http://www.themagicmoment.co.uk. We have also looked into our access logs and found some of the 302 redirect records that read like: "GET /bridal-party-dresses-mother-of-the-bride-dresses_c109?gclid=CI_6gu3us7ACFQcrpAodD3KyUw HTTP/1.1" 302 12818 "[login to view URL]" "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; GTB7.3; BTRS123374; SLCC1; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30618; msn OptimizedIE8;ENNZ)" Not sure if the website has been hacked or there is a security problem with zencart that we do not know about? Thank you for your help!