The Lightning Network was proposed years ago to solve Bitcoin’s transaction speed problems. It is currently under development.
The Lightning Network works by taking the transactions away from the Bitcoin Blockchain. Transactions that happen on the Lightning Network are instant and they can go back and forth several times, when users agree with each other, the transactions come out of the Lightning network into the main Blockchain.
The Lightning Network should reduce fees as well as transaction speed. It basically solves the scalability problem, however, a software engineer working on the network has spotted a few security issues which could cause loss of funds.
The report found here states that the full details will be released in 4 weeks and to please upgrade before then. The details are not disclosed as a security measure.
Clearly the Lightning Network still needs a lot of work, there are other problems present, for instance the possibility of an increase in transaction fees as well as vulnerability to hacks.