I've always considered Pseudococcidae to be scale insects, mostly because of an old Irish gardener I worked for, who called them "Soft Scale." I also see many citations in Google which consider them to be scale. Wikipedia: "Mealybug is the common name of insects in Pseudococcidae, a family of unarmored scale insects found in moist, warm climates." IPM of Alaska: "Mealybugs are part of the insect families collectively known as scale insects." Columbia Encyclopedia: "..common name for certain unarmored scale insects that exude a granular white secretion, giving them a mealy appearance." It seems the more I learn, the less I know.

First of all, I don't have a stash of cigarettes. :P Second, my previous apartment was infested with Indian moth so I actually bought a lot of air tight OXO containers for all my dried food since then. Plus I freeze every dry stuff from grocery store in the freezer for a week before storage. In addition, I don't see these bugs very often. Maybe one or two per two weeks during spring-summer months. Moreover, I found it between the window screen and window (and I don't ever open that window, and the screen is located outside. I took the picture inside my apartment with the window pane in between my camera and the window screen). Hence I believe it's coming from my neighbors. I don't know what I can do in this case. They could be coming from cracks and nooks.

They appear to resemble a type of scale but I am not familiar with a species that remains that flat or attaches to the plant in that manner. But there are scores of different species so not inclined to rule that out. I would suggest you take a sample of a branch or stem with these creatures attached into your county extension office for an accurate ID. They will also be able to tell you how to treat and when. If it is scale, timing is key!!

Top looks like a purple leaved Prunus. Second is a Dogwood.