Which spider is this? Is it dangerous?
It is clearly a Theridiid (cobweb) spider, but it doesn't look like the Parasteatoda tepidariorum I'm familiar with here in the US.  The egg sac it's holding indicates it's a mature female, and the regular pattern on the abdomen is both distinctive and unlike the variable, blotchy pattern of tepidariorum.  Unfortunately, not being familiar with Eurasian spiders likely to be found in your area, I can't be of much help as to what it might be, beyond limiting it to the Theridiids.
Oh, yes - it's pretty clearly not one of the Widows (Latrodectus spp.), and since those are the only medically significant Theridiids we know, it's not dangerous.