Eloqua and variable in URL

Hi,

I'm sending a campaign where i put a variable in my url. The data of my variable is emailEloquaCampaign.

I don't know how, but for some user this data change and became like dbzrotjdisksdfkllkjlfds... This is totaly incomprehensible. How could-it be change like this? And does it come from Eloqua or maybe in next step in outlook?