Try the following:

\w+(?:\.\w+)+

The + after (?: ... ) tell it to match what is inside the parenthesis one or more times.

Note that \w only matches ASCII characters, so a word like café wouldn't be matches by \w+, let alone words/text containing Unicode.

EDIT

The difference between [...] and (?:...) is that [...] always matches a single character. It is called a "character set" or "character class". So, [abc] does not match the string "abc", but matches one of the characters a, b or c.

The fact that \w+[\.\w+]* also matches your string is because [\.\w+] matches a . or a character from \w, which is then repeated zero or more time by the * after it. But, \w+[\.\w+]* will therefor also match strings like aaaaa or aaa............

The (?:...) is, as I already mentioned, simply used to group characters (and possible repeat those groups).

More info on character sets:

More info on groups: