Adw_Adroar.A is an adware program that adds a Browser Helper Object (BHO) to automatically pop up advertisements from certain Web sites affiliated with AdRoar.com, which is an advertisement company.

It also gathers information about the affected user's surfing habits in order to display related advertisements.

This adware usually comes bundled with other adware-enabled applications, which are programs that are offered for free in exchange of pop-up advertisements. It uses the file ARUpdate.exe to automatically update itself. It uses the file ARUpdate.exe to automatically update itself.

Technical details can be found at this Trend Micro page.