Is anyone aware of or has anyone experienced risks associated with using tracking codes? For example, I have used the Alexa tracking code (for confirming site ownership, an example is <!-- 12345678912345 -->) recently, which after uploading my site was entirely blank with no code revealed in 'view source'. I find it important to mention that after reversing these changes it was still affected, and no other changes had been made for weeks. It is common these days for sites such as google analytics, alexa, and so on to require you to insert these codes into your website to use their services. Are the any risks involved in this, if so, what are they? If you have a previous experience yourself, please share.
In the worst case (a tracking code for a badly designed service) this could theoretically reveal your login details for that service.
In the average case (such as google analytics?) I imagine the tracking code is easily identifiable so will reveal that you use that service.
It seems very unlikely that your site turned blank due to insertion of a comment such as the one above; something else has presumably happened there.