#1 - Nov. 26, 2016, 3:17 a.m.
Wowhead is indeed having some major problems right now. Several users are noting that the site uploads potentially several gigabytes of data in a relatively short timeframe, while each individual page load can be numerous megabytes in size. If you are accessing Wowhead from a capped Internet plan, the site can potentially use up all of your data in only a few hours. Likewise, if you are using Wowhead on a slower Internet connection, it can consume a lot of bandwidth in the background and drastically impact your in-game latency.
There is a thread on Wowhead's forum regarding this as well:
Additionally, as usual, be careful in general when browsing Wowhead. Wowhead has gained a notorious reputation for serving up malicious advertisements. When accessing Wowhead, I personally recommend using an ad blocking program such as uBlock Origin for your safety.
Bad advertisements are relatively rare and you are highly unlikely to be affected, but if you notice any strange behaviour with your Battle.net account or are concerned in general, run an occasional malware scan with a program such as Windows Defender or Malwarebytes Anti-Malware.
Stay safe, and have fun!