Number ten: defamatory tweets
Defamation law protects a person's reputation. In England, the law of libel makes it an offence to communicate defamatory remarks where that communication takes some form of permanence (and in Scotland the general law of defamation has the same effect). At least one UK court has given the impression that communications via Twitter have a form of permanence. Defences for truth, honest opinion and providing a public service may apply. However, a claim in libel could result in civil proceedings and claims for damages and costs.
The test: If a tweet lowers a person's standing 'in the estimation of right-thinking members of society' it will breach the law of libel. This may occur where a tweet causes a person to be exposed to 'hatred, ridicule, or contempt', encourages exclusion of that person from society or imputes a lack of professional skill or efficiency.
Number nine: harassing tweets
UK law protects against harassment by means of the Protection from Harassment Act 1997. The legislation provides that "if a reasonable person in possession of the same information would think the course of conduct amounted to or involved harassment" it is harassment. The UK courts have ruled that this could include the publication of words that cause 'alarm' or 'distress'. Two or more tweets would be necessary for a claim of harassment to be made, as it involves a 'course of conduct'. Harassing tweets could result in a claim for damages for anxiety or financial loss, fines or imprisonment for up to six months.
The test: Tweets which the 'reasonable person' would conclude cause alarm or distress may amount to harassment.
Number eight: malicious tweets
Tweets made within the intention of damaging another's business, goods or services through false statements, or which are reckless with the truth as to another's business, goods or services will offend the law against malicious falsehood. A maliciously false tweet could result in a claim for damages for loss and for further compensation for causing distress and 'hurt feelings.'
The test: False tweets with the intent to injure another's commercial interests, or recklessness as to the truth, will amount to malicious falsehood.
Number seven: menacing tweets
A tweet that is grossly offensive, or of an indecent, obscene or menacing character, will offend the Communications Act 2003. The Crown Court considered Paul Chambers' tweet "... I am blowing the airport sky high" to be menacing, however the High Court overturned its decision. The High Court ruled that the Communications Act would not prevent satirical, iconoclastic, or rude comment, expression of the unpopular, unfashionable opinion about serious or trivial matters, humour, comments that are distasteful or even painful to those subjected to them, silly jokes or jokes in bad taste that a person would be likely to brush aside or empty bombastic or ridiculous banter. A tweet that is indecent, obscene or menacing in character could result in a fine or a prison sentence of up to six months.
The test: If a tweet could create fear or apprehension in the minds of anyone who may reasonably be expected to see it the tweet could be considered a menace and an offence under the Communications Act.
Number six: deceptive tweets (and other misrepresentations)
A tweet containing a false statement that induces another person to act on it may offend laws against deceit and the making of misrepresentations. A duty may also arise for a professional or other skilled person not to make careless tweets. Misleading commercial communications may offend either the Consumer Protection from Unfair Trading Regulations 2008, the Business Protection from Misleading Marketing Regulations 2008 and industry based advertising rules. Untrue tweets in a commercial context can result in damages claims and prison sentences of up to two years.
The test: Is the tweet deceptive in nature or likely to deceive?
Number five: impersonating tweets
The Fraud Act 2006 protects against fraudulent activities. An impersonator who opens a Twitter account could be exposed to a claim for fraud if the person who has been impersonated suffers loss or damage as a result of the impersonation. A claim for fraud can result in criminal charges with a penalty of up to 10 years imprisonment and fines.
Test: Misleading or an untrue representation as to a person's identity on twitter could amount to fraud.
Number four: threatening tweets
A tweet could amount to an assault if the person to whom it was directed has a genuine belief that physical harm is imminent. A series of tweets which cause psychological damage to another person may also offend UK criminal law. Criminal sanctions would apply in these cases. A tweet could also amount to intimidation if the tweeter makes a threat to engage in unlawful conduct (for example, violence, destroying property or in some circumstances breaching contractual obligations), which coerces another person into doing something for which they suffer loss or damage. The tweet must however be more than "idle abuse" to offend the law of intimidation. An intimidating tweet could result in a claim for compensation for loss or damages suffered.
The test: Generally, an intention to cause harm or intimidation may offend either criminal or civil wrong laws.
Number three: tweets revealing personal or confidential information
Data protection laws protect against processing of personal information without permission. The rules do not apply to purely personal and household activities. It is unclear whether statements made on twitter could ever be said to be 'purely personal or of a household nature.' Where they are not, there is a risk that data protection laws may be breached if consent is not obtained before revealing another person's personal information. The penalty for breaching data protection laws vary across Europe. In the UK, a breach of data protection laws may result in fines and criminal convictions.
Particularly in the employer-employee context, a person may be bound to keep information of another confidential. A tweet breaching any such obligation could result in a claim for damages or an account of profits for any income made as resulting from the exposed information.
Test: Tweets revealing personal details about another person without their consent may breach data protection laws.
Number two: copied tweets
A tweet could offend copyright law if it reproduces even part of an isolated sentence from a copyright work. Copyright law has changed dramatically over the last few years. Generally, UK laws tended to look at whether a substantial part of a copyright work had been reproduced, publicly made available, distributed, translated or adapted without a copyright holders consent. Substantiality was measured both qualitatively and quantitatively. UK laws also concentrated on whether skill, judgement and labour went into the preparation of a work before concluding that copyright subsists in it. However the effect of a recent European Court of Justice (ECJ) decision, which UK law must conform to, may mean that isolated sentences must be looked at disjunctively from a whole copyright work in order to determine whether an infringement has occurred. Further ECJ decisions have suggested that rather than look for skill, judgement or labour in putting words together, there must be an assessment of whether or not an author has exercised creative choices in the form of intellectual effort in arranging words, images or sounds. Claims for damages for loss suffered and criminal charges with prison sentences of up to two years can result from a tweet that infringes copyright law.
The test: A tweet which reproduces the work of another without consent will offend copyright law if that work gives evidence of another's creative choices in arranging words, images or sounds.
Number one: branded tweets and hashtags
Hashtags, marked with the '#' symbol, are used in order to alert users to relevant conversations taking place on Twitter. There is a risk, however, that combining a hashtag with the trade mark of another person could result in trade mark infringement. Trade mark law generally protects the trade mark owner against use of its trade mark without permission in a way that may create a likelihood of confusion or association with other similar products or services. Where a trade mark has a significant established reputation, the protection will extend to association with any products or services (not merely similar ones) in a manner that amounts to taking an unfair advantage or is detrimental to the distinctive character or repute of the established mark. Use of hashtags in these circumstances potentially could result in a damages claim.
The test: Does the use of a hashtag create a likelihood of association or confusion with the products or services of a trade mark owner?
Twitter raises important issues about privacy, free speech, censorship and individual rights and responsibilities. Of course, there is nothing stopping a person from self-incriminating themselves by tweets revealing illegal conduct such as the reports of a doctor on sick leave. The balance struck by UK law will differ from that struck in other places. Twitter users in both commercial and non-commercial contexts should understand this balance.
Luke Scanlon is a technology law expert at Pinsent Masons, the law firm behind Out-Law.com
Editor's note: Updated 10 August 2012 to reflect a majority view that the effect of the Coroners and Justice Act 2009 leaves little if any room for criminal libel.