googletagmanager.comは安全ですか？

It involves tracking, profiling, sharing to undisclosed 3rd parties and co-operation with advertisers (although Doubleclick is nowdays Google's own, isn't it?). This according to information from Ghostery. It has no benefit to user, it runs unnecessary scripts (wasting your machine resources) and can't be trusted privacy vise. Just check this out: *****

The reason for the low rating is tracking by Google is especially egregious because of their sheer size. It is my opinion that nobody should have that level of power over everybody else. Blocked.

"Tags are tiny bits of website code that let you measure traffic and visitor behavior, understand the impact of online advertising and social channels, use remarketing and audience targeting, test and improve your site, and more." -- ***** This domain is used for campaign marketing and customer behavioral analytics (tracking). This domain can be treated like other Google ad or analytics services and falls under the same privacy policies. I keep this domain blocked.

This is a script server website. If you trust the client's site, then you should be able to trust the third party scripts. My preference is not to allow third party scripts unless they are required to display the client's website content. I use Firefox and NoScript. As this is a business website, it is not suitable for children.

The standard, blanket Google services rhetoric applies here. This site is a service backbone for Google Tag Manager (http://www.google.com/tagmanager/). Google, by-and-large, is a good company; however, do keep in mind that any and all Google services use the now-unified Google privacy policy, which many consider to be invasive.