All Bitcoin private keys is simply an integer number between 1 and 1.157.920.892.373.161.954.235.709.850.086.879.078.528.375.642.790.749.043.826.051.631.415.181.614 inclusive (slightly less than 2^256 ). Yes, this is an unfathomably large number. It is approximately 10^77 in decimal. The visible universe is estimated to contain 10^80 atoms. That has a minimal chance, near zero, to repeat private keys randomly when you generate new Bitcoin address. But we have a leak threat some private keys. For instance: easy generated keys, available internet, simple words of Brain wallet, vulnerability of databases and etc.
We created a website www.AllPrivateKeys.com with a whole range of Bitcoin private keys and addresses. We just iterate whole integer range of keys, generate private keys in WIF (Wallet Import/Export Format) and make Bitcoin Addresses. You can shift to any page and see preferred period of addresses. Also there is a vulnerability of a variety private wallet’s keys for Search engines like Google, Yahoo, Bing and others. Some pages are indexed and keys leaked to search engine, but it's too huge volume of database to store whole keys and addresses. It's about 10^69 Terabytes. Currently, nobody has even had a hard drive with such kind of volume.By the way, Bitaps security team collects and generates leaked databases with the rules below:
Our database has more than 2 million rows of potential leaked addresses (some of them are without transactions). Total count of all used Bitcoin addresses is about 156.268.373 (by 21 Jun 2016) addresses.
Checking your Bitcoin address at www.AllPrivateKeys.com for private key leak is safe for you. Because this information is available and it cannot perform any problems.
And if your private key is in secure, we can monitor and notify you about any leaks by email. Because the Bitcoin community is honest and reliable!