Pixiv.net safe?

Hello. Last night, my brother used a website called pixiv.net which gave him problems with Internet explorer, like it wouldn’t perform properly. I was unfamiliar with the site, so I scanned it on a number of websites. Many of them came up clean, except for one in particular. sitecheck.sucuri.net. It said that there were a number of hidden iframes in the site. So, how dangerous could this be? Thanks.