Leaving it is the best decision. Here's the license:
8. Interaction with Third Party Sites and Services
The SweetIM Software and Service may allow you to interact with third-party Web sites and Web services ("Link(s)"). The Links are not under the control of Macrogaming and Macrogaming is not responsible for the contents of any Links, including without limitation any link contained in a Link, or any changes or updates to a Link. Macrogaming is not responsible for any form of transmission received from any Link, nor is Macrogaming responsible if the Link is not working appropriately. Macrogaming is providing these Links to you only as a convenience, and the inclusion of any Link does not imply endorsement by Macrogaming of the Link or any association with its operators. You are responsible for viewing and abiding by any privacy statements and terms of use posted in connection with the Links.
You are solely responsible for any dealings with third parties (including advertisers) who support the Service, including the delivery of and payment for goods and services.
So it's not spyware or a virus but it is adware, therefore it will probably nag you. Nothing fishy since installing such software would be a willful choice of yours, but probably it wouldn't be a wise choice.