Series.iloc[ negative number ] can access memory it doesn't own or cause Segmentation Fault
In other words, there is no bounds checking for Series.iloc[] with a negative argument. It just accesses whatever is in the memory there. Also a security breach.

It does appear to check on write, just not on read.

Python 2.7.10 |Anaconda 2.1.0 (64-bit)| (default, May 28 2015, 17:02:03) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux2
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> > > import pandas as pd
> > > pd>>> pd.**version**
> > > '0.16.2'
> > > s = pd.Series([1,2,3])
> > > s
> > > 0    1
> > > 1    2
> > > 2    3
> > > dtype: int64
> > > s.iloc[-2]
> > > 2
> > > s.iloc[-4]
> > > 33
> > > s.iloc[-12345]
> > > 0
> > > s.iloc[-123123123123123]
> > > Segmentation fault (core dumped)
