Hamming distance measures the minimum number of substitutions required to change one string into the other, or the minimum number of errors that could have transformed one string into the other. It is also known as edit distance between two strings.
For binary strings $a$ and $b$ the Hamming distance is equal to the number of ones in $a \oplus b$.
Lets consider a code $C$ and minimum hamming distance between any of its codewords be $\lambda$.
1. A code $C$ is said to be $k$ errors detecting iff $ \lambda\geq k+1 $.
It can detect error upto edit distance of $k$.
$$k\leq\lambda-1$$
So this code can detect an error of at most $\lambda-1$ edit distance.
2. A code $C$ is said to be $k$ errors correcting iff $ \lambda\geq 2k+1 $.
It can correct error upto edit distance of $k$.
$$k\leq \lfloor\frac{\lambda-1}{2}\rfloor$$
So this code can correct an error of at most $\lfloor\frac{\lambda-1}{2}\rfloor$ edit distance.
Now coming back to the question, here $\lambda = 4$
Thus we can detect maximum error of $4-1=3$ bits.
And can correct maximum error of $\lfloor\frac{4-1}{2}\rfloor=1$ bit.
source: Error_detection_and_error_correction
