Although it is technically impossible to own more than 100% of shares issued by a company, often times data sources will display the institutional investors' percentage ownership as exceeding 100%. The reason for this discrepancy is that there is noise within the data. Typically there are two main sources of this noise.
1) The data used to configure the statistic is derived from reports submitted by institutions and these reports can have different holding dates. The data within these reports are also typically reported once a month and can have a lag of 4 weeks.
2) The way in which investors report the ownership of the shares can also result in noisy data. For example, hypothetical company XYZ issues 10 million shares which are all owned by institutional investor A. institutional investor B borrows 5 million shares to sell to investor C so that investor can take a short position. If both A and B claim ownership of the 5 million shares then the percentage ownership reported would be (15 million shares /10 million shares) = 150%