Shoo Flies UPDATED

When I woke up yesterday, I got up and started to put together my breakfast.  As I was moving about in the kitchen, I noticed several houseflies zooming about.  My usual reaction to houseflies is to ignore them since they're hard kill and their adult lifespan is so short.  However, I could see that there were about five or six flies moving through the air, so I grabbed my sandals and started working to smash them. I counted how many I was eliminating, but lost count after I hit eleven.  It seemed like every time I turned around, more flies were appearing.  I decided to finish making and eating breakfast, then I would turn my complete attention to killing the flies.

Having consumed my meal, walked back into the living room and saw that the lamp next to my bed (since I sleep on sofa-bed) was covered in at least another two dozen flies.  Did your skin just crawl reading that?  I almost lost my breakfast when I saw the state of things.  I decided to grab the vacuum and suck them up.  It a took a while, but finally sucked them all up.  I then went back to clean the dishes from breakfast and found two more flies.  I killed them, but in the process found another three, which I also killed.  As things stand, I know of at least one fly that's still alive, because I can hear it buzzing, and I suspect that there's at least a few more on top of that.

Flies are super-gross on their own, but they also attract spiders and other predators that I really, really don't want in my home.  I keep my apartment clean and rarely open the windows, so this was really surprising.  I plan on talking to my landlord tomorrow about this because having over three dozen flies in my apartment is absolutely unacceptable.

UPDATE:
It turns out, one of my windows was installed incorrectly.  One of the maintenance guys came down and took a look at everything and fixed the problem.  He said that with our severe weather fluctuations lately, the flies were seeking warmth and since I had a window that wasn't installed correctly, they were able to squeeze in.  Since I don't have anything decomposing for them to eat, they were hanging out at the nearest light source.

I am happy to say that with the window fixed and using both a flyswatter and the vacuum, I am currently fly-free.  All told, I killed about six or seven dozen flies.  Although, there is a particularly acidic smell in the air, so I'm guessing that there's a lot of fly feces in my apartment now.  Good thing I was planning on giving the place a deep cleaning anyway.

And since the question was asked, these were not small fruit flies, but their larger classmates, houseflies.