Sigma 17-70mm F2.8-4 DC Macro
If you just bought it send it to Sigma for repair. It's free of charge and they will take care of the problem.
Bought 2 Sigma's (17-70 OS and 18-250 OS), the superzoom had the sticker at the box.
At both cases AF and aperture were not properly working. The first lens was changed and the second did get a software update. Both are working flawless since then.
There service is very good (here in Germany at least), would never hesitate to buy again.