This is a harmless glitch caused by recent server-side alerts additions by LL. The next releases will have the corresponding messages added to the notification.xml UI file (i.e. you will see a proper, plain text, explanatory dialog for these alerts). However, the alert itself cannot be removed/skipped: it is the result of something that did happen to your avatar since last login or that happens at login time (here, an object rezzed on the parcel where you last logged out TPed your avatar home).
This is probably an issue with your firewall settings (make sure your firewall doesn't block any of the viewer's ports, neither SLPlugin and the associated webkit plugin), or possibly an anti-virus software getting illegally in the way. Try loading the following URLs from a web browser and see what happens:
If they load in your web browser, they also should load in the viewer (provided your firewall doesn't block the latter and that no anti-virus is blocking SLPlugin and the webkit media plugin used by the viewer). If they don't, you've got a routing issue (could be a bad DNS, or a broken router at your ISP's end).