Hashtag hijacking

Using hashtags on Twitter (using # before a keyword to show your subject, allowing others to follow) is extremely useful.
For example following the stream of collective opinion on last night's BBC Question Time was both amusing and insightful. (#bbcqt)
However today when searching subsequent views on the programme, there are now a whole host of unrelated sales messages using the same hash tag. Obviously realising that those following this important subject on Twitter may be influential decision makers, spam accounts have decided to invade this subject for gain.

Take out:

• Organisers- create a topical hashtag for your important event, but expect to use another for your next one
• Followers - follow a hashtag, but don't expect the same quality of tweets in the morning
• Twitter - please find some way of stopping this or see the decline in the usefulness of hashtags